Update Geo docs for selective sync changes

HTTP is supported while SSH is coming.

doc/administration/geo/replication/configuration.md

@@ -314,6 +314,19 @@ It is important to note that selective synchronization:
      Selective synchronization restrictions are implemented on the **secondary** nodes,
      not the **primary** node.
 
+### Git operations on unreplicated respositories
+
+> [Introduced](https://gitlab.com/groups/gitlab-org/-/epics/2562) in GitLab 12.10.
+
+Git clone, pull, and push operations over HTTP(S) are supported for repositories that
+exist on the **primary** node but not on **secondary** nodes. This situation can occur
+when:
+
+- Selective synchronization does not include the project attached to the repository.
+- The repository is actively being replicated but has not completed yet.
+
+SSH [support is planned](https://gitlab.com/groups/gitlab-org/-/epics/2562).
+
 ## Upgrading Geo
 
 See the [updating the Geo nodes document](updating_the_geo_nodes.md).

doc/administration/geo/replication/index.md

@@ -244,6 +244,7 @@ CAUTION: **Caution:**
 This list of limitations only reflects the latest version of GitLab. If you are using an older version, extra limitations may be in place.
 
 - Pushing directly to a **secondary** node redirects (for HTTP) or proxies (for SSH) the request to the **primary** node instead of [handling it directly](https://gitlab.com/gitlab-org/gitlab/issues/1381), except when using Git over HTTP with credentials embedded within the URI. For example, `https://user:password@secondary.tld`.
+- Cloning, pulling, or pushing repositories that exist on the **primary** node but not on the **secondary** nodes where [selective synchronization](configuration.md#selective-synchronization) does not include the project is not supported over SSH [but support is planned](https://gitlab.com/groups/gitlab-org/-/epics/2562). HTTP(S) is supported.
 - The **primary** node has to be online for OAuth login to happen. Existing sessions and Git are not affected.
 - The installation takes multiple manual steps that together can take about an hour depending on circumstances. We are working on improving this experience. See [Omnibus GitLab issue #2978](https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2978) for details.
 - Real-time updates of issues/merge requests (for example, via long polling) doesn't work on the **secondary** node.