update docs

changelogs/unreleased-ee/feature-ldap-group-filter.yml

+---
+title: Add LDAP synchronization based on filter for GitLab groups
+merge_request:
+author:
+type: added

doc/administration/auth/ldap-ee.md

@@ -54,9 +54,12 @@ new groups they might be added to when the user logs in. That way they don't nee
 to wait for the hourly sync to be granted access to the groups that they are in
 in LDAP.
 
-If `group_base` is set in LDAP configuration, a group sync process will run
-every hour, on the hour. This allows GitLab group membership to be automatically
-updated based on LDAP group members.
+We can also add a GitLab group to sync with one or multiple LDAP groups or we can
+also add a filter. The filter must comply with the syntax defined in [RFC 2254](https://tools.ietf.org/search/rfc2254). 
+
+A group sync process will run every hour on the hour, and `group_base` must be set
+in LDAP configuration for LDAP synchronizations based on group CN to work. This allows
+GitLab group membership to be automatically updated based on LDAP group members.
 
 The `group_base` configuration should be a base LDAP 'container', such as an
 'organization' or 'organizational unit', that contains LDAP groups that should
@@ -97,8 +100,9 @@ production:
 
 To take advantage of group sync, group owners or masters will need to create an
 LDAP group link in their group **Settings -> LDAP Groups** page. Multiple LDAP
-groups can be linked with a single GitLab group. When the link is created, an
-access level/role is specified (Guest, Reporter, Developer, Master, or Owner).
+groups and/or filters can be linked with a single GitLab group. When the link is
+created, an access level/role is specified (Guest, Reporter, Developer, Master,
+or Owner).
 
 ## Administrator Sync