Document the steps to update the CodeMirror release zip file

Change-Id: I6f16a4587473022edddce22a508b6c074f90c043

Documentation/dev-contributing.txt

diff --git a/Documentation/dev-contributing.txt b/Documentation/dev-contributing.txt
index c356dab..f5caf40 100644
--- a/Documentation/dev-contributing.txt
+++ b/Documentation/dev-contributing.txt
@@ -336,6 +336,33 @@
 * Update to the same GWT version in the `gwtjsonrpc` project, and release a
 new version.
 
+=== Updating to new version of CodeMirror
+
+* Clone the git from https://github.com/codemirror/CodeMirror
+* Checkout the version needed
+* If the needed version is not a tagged version, use `git describe` to determine
+the version number:
++
+----
+ git describe --tags
+----
+
+* Create the release zip file:
++
+----
+ git archive --format=zip --prefix=codemirror-4.10.0-6-gd0a2dda/ d0a2dda > 4.10.0-6-gd0a2dda.zip
+----
+
+* Determine the sha1 hash of the zip file:
++
+----
+ openssl sha1 4.10.0-6-gd0a2dda.zip
+----
+
+* Upload the zip file to the
+link:https://console.developers.google.com/project/164060093628/storage/gerrit-maven/[
+gerrit-maven] storage bucket
+
 GERRIT
 ------
 Part of link:index.html[Gerrit Code Review]