DashboardBuilders: document required connectivity to Google Cloud Storage

Gomote creation cannot work without, so include it in the list.

For golang/go#72869.

Change-Id: Id54f3aa32259c3b298b26eb51c881d90dc759ae9
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/657975
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>

Author: dmitshur

DashboardBuilders.md

@@ -17,6 +17,7 @@ The LUCI system requires builders to run two applications which authenticate to
     - https://cr-buildbucket.appspot.com
     - https://7419-34ac013-dot-chromium-swarm.appspot.com (possible changed in the future?)
     - https://remotebuildexecution.googleapis.com
+    - https://storage.googleapis.com (for [gomote creation](https://cs.opensource.google/go/x/build/+/master:internal/gomote/swarming.go;l=1048;drc=3ff389173c43ad07048563029b575ab7ec0df5da))
   * Resources
     - At least 512MB of memory. 1GB or more is highly recommended.
     - 20GB disk space is ideal.