dev-release: Document update api version in bazlets repository

Change-Id: Iec0a5e948dc4928c483d4d61327e65a45c88aa49
diff --git a/Documentation/dev-release.txt b/Documentation/dev-release.txt
index 26193f4..2f6a7d6 100644
--- a/Documentation/dev-release.txt
+++ b/Documentation/dev-release.txt
@@ -359,6 +359,13 @@
   git merge stable
 ----
 
+[[update-api-version-in-bazlets-repository]]
+
+Bazlets is used by gerrit plugins to simplify build process. To allow the
+new released version to be used by gerrit plugins,
+link:https://gerrit.googlesource.com/bazlets/+/master/gerrit_api.bzl#8[gerrit_api.bzl]
+must reference the new version. Upload a change to bazlets repository with
+api version upgrade.
 
 GERRIT
 ------