Merge branch 'ldap_docs' into 'master'

Clarify LDAP group sync

This documents LDAP group sync details. When group sync is enabled, non LDAP users will not be removed. They may leave on their own. However, no one can add or remove users manually.

cc/ @balameb @axil 

See merge request !85

doc/integration/ldap.md

@@ -200,8 +200,10 @@ If you accidentally lock yourself out of your own GitLab group, ask another owne
 
 ### Non-LDAP GitLab users
 
-Your GitLab instance may have users on it for whom LDAP is not enabled.
-If this is the case, these users will not be affected by LDAP group synchronization settings: they will be neither added nor removed automatically.
+If there are also non-LDAP users in your GitLab instance, they will remain
+members of the GitLab group until they choose to leave the group on their own.
+Administrators, owners, and masters cannot add or remove users from GitLab
+groups when LDAP group sync is enabled.
 
 ### ActiveDirectory nested group support