Update step 5 "database" (Issue #2894)

Made it a bit clearer what step 5 is for to stop people skipping it. This time with a relative link.

doc/install/installation.md

@@ -174,7 +174,7 @@ and make sure you have followed all of the above steps carefully.
 # 5. Database
-See `doc/install/databases.md`
+To setup the MySQL/PostgreSQL database and dependencies please see [`doc/install/databases.md`](./databases.md) .
 # 6. GitLab