Harmonizes titles between two Geo landing pages

Menu entries in global navigation will be updated to match.

doc/administration/geo/disaster_recovery/index.md

-# Disaster Recovery **(PREMIUM ONLY)**
+# Disaster Recovery (Geo) **(PREMIUM ONLY)**
 Geo replicates your database, your Git repositories, and few other assets.
 We will support and replicate more data in the future, that will enable you to

doc/administration/geo/replication/index.md

-# Geo Replication **(PREMIUM ONLY)**
+# Replication (Geo) **(PREMIUM ONLY)**
 > - Introduced in GitLab Enterprise Edition 8.9.
 > - Using Geo in combination with
@@ -6,7 +6,7 @@
 >   is considered **Generally Available** (GA) in
 >   [GitLab Premium](https://about.gitlab.com/pricing/) 10.4.
-Geo is the solution for widely distributed development teams.
+Replication with Geo is the solution for widely distributed development teams.
 ## Overview