Mention tagging in the release process

Change-Id: I42820a16217e4b409e76f0c74b828eac58153355

Documentation/developer-guide.md

diff --git a/Documentation/developer-guide.md b/Documentation/developer-guide.md
index 629cda1..516dac0 100644
--- a/Documentation/developer-guide.md
+++ b/Documentation/developer-guide.md
@@ -129,6 +129,8 @@
 ./tools/maven/mvn.sh deploy
 ```
 
+Tag the release with an annotated tag matching the version number.
+
 Once released, Maven projects can consume the new version as long as they point
 at the proper repository URL. Similarly, Bazel projects using the `maven_jar`
 bazlet can use the new version with `repository = GERRIT`.