Merge branch 'howto-in-docs' into 'master'

Howto In Docs

Added 3/5 issues to the docs.
The other issues didn't make sense to add here ( a reference to other docs that was already there and an explanation of a feature -> features shouldn't be explained here)

@sytse you can close the issue tracker on the subscriber gitlab-ee repo

doc/install/ldap.md

+# Link LDAP Groups
+You can link LDAP groups with GitLab groups.
+It gives you ability to automatically add/remove users from GitLab groups based on LDAP groups membership.
+
+How it works: 
+1. We retrieve user ldap groups
+2. We find corresponding GitLab groups
+3. We add user to GitLab groups
+4. We remove user from GitLab groups if user has no membership in LDAP groups
+
+In order to use LDAP groups feature:
+
+1. Edit gitlab.yml config LDAP sections.
+2. Visti group settings -> LDAP tab
+3. Edit LDAP cn and access level for gitlab group
+4. Setup LDAP group members
+
+
+Example of LDAP section from gitlab.yml
+
+```
+  #
+  # 2. Auth settings
+  # ==========================
+
+  ## LDAP settings
+  ldap:
+    enabled: true
+    host: 'localhost'
+    base: 'ou=People,dc=gitlab,dc=local'
+    group_base: 'ou=Groups,dc=gitlab,dc=local'
+    port: 389
+    uid: 'uid'
+```
+
+
+# Test whether LDAP group functionality is configured correctly
+
+You need a non-LDAP admin user (such as the default admin@local.host), an LDAP user (e.g. Mary) and an LDAP group to which Mary belongs (e.g. Developers).
+
+1. As the admin, create a new group 'Developers' in GitLab and associate it with the Developers LDAP group at gitlab.example.com/admin/groups/developers/edit .
+2. Log in as Mary.
+3. Verify that Mary is now a member of the Developers group in GitLab.
+
+If you get an error message when logging in as Mary, double-check your `group_base` setting in `config/gitlab.yml`. 
+
+
+# Debug LDAP user filter with ldapsearch
+
+This example uses [ldapsearch](http://www.openldap.org/software/man.cgi?query=ldapsearch&apropos=0&sektion=0&manpath=OpenLDAP+2.0-Release&format=html) and assumes you are using ActiveDirectory.
+
+The following query returns the login names of the users that will be allowed to log in to GitLab if you configure your own `user_filter`.
+
+```bash
+ldapsearch -H ldaps://$host:$port -D "$bind_dn" -y bind_dn_password.txt  -b "$base" "(&(ObjectClass=User)($user_filter))" sAMAccountName
+```
+
+- `$var` refers to a variable from the `ldap` section of your `config/gitlab.yml` https://gitlab.com/subscribers/gitlab-ee/blob/master/config/gitlab.yml.example#L100;
+- Replace `ldaps://` with `ldap://` if you are using the `plain` authentication method;
+- We are assuming the password for the `bind_dn` user is in `bind_dn_password.txt`.