Merge branch 'docs/ssot_groups_index' into 'master'

Edit *Groups index* for SSOT guidelines

See merge request gitlab-org/gitlab-ce!29173

doc/user/group/index.md

+---
+type: reference, howto
+---
+
 # Groups
 
 With GitLab Groups you can assemble related projects together
@@ -9,7 +13,7 @@ Find your groups by clicking **Groups > Your Groups** in the top navigation.
 
 ![GitLab Groups](img/groups.png)
 
-> The groups dropdown in the top navigation was [introduced][ce-36234] in [GitLab 11.1](https://about.gitlab.com/2018/07/22/gitlab-11-1-released/#groups-dropdown-in-navigation).
+> [Introduced][ce-36234] in [GitLab 11.1](https://about.gitlab.com/2018/07/22/gitlab-11-1-released/#groups-dropdown-in-navigation)
 
 The Groups page displays:
 
@@ -364,5 +368,17 @@ With [GitLab Issues Analytics](issues_analytics/index.md), you can see a bar cha
 
 Use GitLab as a [dependency proxy](dependency_proxy/index.md) for upstream Docker images.
 
+<!-- ## Troubleshooting
+
+Include any troubleshooting steps that you can foresee. If you know beforehand what issues
+one might have when setting this up, or when something is changed, or on upgrading, it's
+important to describe those, too. Think of things that may go wrong and include them here.
+This is important to minimize requests for support, and to avoid doc comments with
+questions that you know someone might ask.
+
+Each scenario can be a third-level heading, e.g. `### Getting error message X`.
+If you have none to add when creating a doc, leave this section in place
+but commented out to help encourage others to add to it in the future. -->
+
 [ee]: https://about.gitlab.com/pricing/
 [ee-2534]: https://gitlab.com/gitlab-org/gitlab-ee/issues/2534