Merge branch 'from_own_instance' into 'master'

added info about migrating to gitlab.com

Added useful information. Because of tweet https://twitter.com/A_Makedonsky/status/610860840036749314

See merge request !1870

doc/workflow/importing/README.md

@@ -4,3 +4,6 @@
 2. [GitHub](import_projects_from_github.md)
 3. [GitLab.com](import_projects_from_gitlab_com.md)
 4. [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.
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