Link to doc about performing a merge

After getting merge approval, it can be hard to find details of how,
exactly, one merges a change into a branch. Since merge requests
automatically link to docs/process/merge_request.md, have a link from
there to the doc with the technical details.

Bug: None
Change-Id: I429064fa06c6b0562d15584c14c04a8347cbafff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2783154
Auto-Submit: Ian Barkley-Yeung <[email protected]>
Reviewed-by: Alex Mineer <[email protected]>
Commit-Queue: Alex Mineer <[email protected]>
Cr-Commit-Position: refs/heads/master@{#869642}
diff --git a/docs/process/merge_request.md b/docs/process/merge_request.md
index 0905103..e750053 100644
--- a/docs/process/merge_request.md
+++ b/docs/process/merge_request.md
@@ -154,3 +154,10 @@
 
 Manual merge reviews will be performed by release
 owners and TPMs.
+
+## Merge Process
+
+Once the merge has been approved, please see
+[How to merge a change to a release
+branch](https://sites.google.com/a/chromium.org/dev/developers/how-tos/drover)
+for technical details on performing the merge.