Update release process

docs/release-process.md

@@ -136,6 +136,9 @@ Finally, for **Mainline** releases only:
 * Merge the branch you are on into `latest_release_doc_updates` and push to GitHub.
 * Close the [milestone](https://github.com/weaveworks/weave/milestones) in GitHub and create the next milestone
 * Update the `#weavenetwork` topic heading on freenode (requires 'chanops' permission)
+* For a mainline release vX.Y.0, create a release branch X.Y from the
+  tag and push to GitHub - this will result in X.Y.0 site docs being
+  published to https://www.weave.works
 
 ## Troubleshooting