[ci skip] Add SVN to Git migration documentation

doc/README.md

@@ -7,6 +7,7 @@
 - [GitLab Basics](gitlab-basics/README.md) Find step by step how to start working on your commandline and on GitLab.
 - [Importing to GitLab](workflow/importing/README.md).
 - [Markdown](markdown/markdown.md) GitLab's advanced formatting system.
+- [Migrating from SVN](migration/README.md) Convert a SVN repository to Git and GitLab
 - [Permissions](permissions/permissions.md) Learn what each role in a project (guest/reporter/developer/master/owner) can do.
 - [Profile Settings](profile/README.md)
 - [Project Services](project_services/project_services.md) Integrate a project with external services, such as CI and chat.

doc/workflow/README.md

@@ -19,3 +19,4 @@
 - ["Work In Progress" Merge Requests](wip_merge_requests.md)
 - [Merge When Build Succeeds](merge_when_build_succeeds.md)
 - [Manage large binaries with Git LFS](lfs/manage_large_binaries_with_git_lfs.md)
+- [Importing from SVN, GitHub, BitBucket, etc](importing/README.md)

doc/workflow/importing/README.md

 # Migrating projects to a GitLab instance
 
 1. [Bitbucket](import_projects_from_bitbucket.md)
-2. [GitHub](import_projects_from_github.md)
-3. [GitLab.com](import_projects_from_gitlab_com.md)
-4. [FogBugz](import_projects_from_fogbugz.md)
-4. [SVN](migrating_from_svn.md)
+1. [GitHub](import_projects_from_github.md)
+1. [GitLab.com](import_projects_from_gitlab_com.md)
+1. [FogBugz](import_projects_from_fogbugz.md)
+1. [SVN](migrating_from_svn.md)
 
-### Note
-* If you'd like to migrate from a self-hosted GitLab instance to GitLab.com, you can copy your repos by changing the remote and pushing to the new server; but issues and merge requests can't be imported.
+In addition to the specific migration documentation above, you can import any
+Git repository via HTTP from the New Project page. Be aware that if the
+repository is too large the import can timeout.
+
+### Migrating from self-hosted GitLab to GitLab.com
+
+You can copy your repos by changing the remote and pushing to the new server;
+but issues and merge requests can't be imported.
 
-* You can import any Git repository via HTTP from the New Project page.
-If the repository is too large, it can timeout. 

doc/workflow/importing/migrating_from_svn.md

 # Migrating from SVN to GitLab
 
-SVN stands for Subversion and is a version control system (VCS).
-Git is a distributed version control system.
+Subversion (SVN) is a central version control system (VCS) while
+Git is a distributed version control system. There are some major differences
+between the two, for more information consult your favorite search engine.
 
-There are some major differences between the two, for more information consult your favorite search engine.
+If you are currently using an SVN repository, you can migrate the repository
+to Git and GitLab. We recommend a hard cut over - run the migration command once
+and then have all developers start using the new GitLab repository immediately.
+Otherwise, it's hard to keep changing in sync in both directions. The conversion
+process should be run on a local workstation.
 
-Git has tools for migrating SVN repositories to git, namely `git svn`. You can read more about this at
-[git documentation pages](https://git-scm.com/book/en/Git-and-Other-Systems-Git-and-Subversion).
+Install `svn2git`. On all systems you can install as a Ruby gem if you already
+have Ruby and Git installed.
 
-Apart from the [official git documentation](https://git-scm.com/book/en/Git-and-Other-Systems-Migrating-to-Git) there is also
-user created step by step guide for migrating from SVN to GitLab.
+```bash
+sudo gem install svn2git
+```
 
-[Benjamin New](https://github.com/leftclickben) wrote [a guide that shows how to do a migration](https://gist.github.com/leftclickben/322b7a3042cbe97ed2af). Mirrors can be found [here](https://gitlab.com/snippets/2168) and [here](https://gist.github.com/maxlazio/f1b593b0d00aa966e9ca).
+On Debian-based Linux distributions you can install the native packages:
+
+```bash
+sudo apt-get install git-core git-svn ruby
+```
+
+Optionally, prepare an authors file so `svn2git` can map SVN authors to Git authors.
+If you choose not to create the authors file then commits will not be attributed
+to the correct GitLab user. Some users may not consider this a big issue while
+others will want to ensure they complete this step. If you choose to map authors
+you will be required to map every author that is present on changes in the SVN
+repository. If you don't, the conversion will fail and you will have to update
+the author file accordingly. The following command will search through the
+repository and output a list of authors.
+
+```bash
+svn log --quiet | grep -E "r[0-9]+ \| .+ \|" | cut -d'|' -f2 | sed 's/ //g' | sort | uniq
+```
+
+Use the output from the last command to construct the authors file.
+Create a file called `authors.txt` and add one mapping per line.
+
+```
+janedoe = Jane Doe <janedoe@example.com>
+johndoe = John Doe <johndoe@example.com>
+```
+
+If your SVN repository is in the standard format (trunk, branches, tags,
+not nested) the conversion is simple. For a non-standard repository see
+[svn2git documentation](https://github.com/nirvdrum/svn2git). The following
+command will checkout the repository and do the conversion in the current
+working directory. Be sure to create a new directory for each repository before
+running the `svn2git` command. The conversion process will take some time.
+
+```bash
+svn2git https://svn.example.com/path/to/repo --authors /path/to/authors.txt
+```
+
+If your SVN repository requires a username and password add the
+`--username <username>` and `--password <password` flags to the above command.
+`svn2git` also supports excluding certain file paths, branches, tags, etc. See
+[svn2git documentation](https://github.com/nirvdrum/svn2git) or run
+`svn2git --help` for full documentation on all of the available options.
+
+Create a new GitLab project, where you will eventually push your converted code.
+Copy the SSH or HTTP(S) repository URL from the project page. Add the GitLab
+repository as a Git remote and push all the changes. This will push all commits,
+branches and tags.
+
+```bash
+git remote add origin git@gitlab.com:<group>/<project>.git
+git push --all origin
+```
 
 ## Contribute to this guide
-We welcome all contributions that would expand this guide with instructions on how to migrate from SVN and other version control systems.
+We welcome all contributions that would expand this guide with instructions on
+how to migrate from SVN and other version control systems.
+
+