dev-release: Create signed tags for the release

Instead of creating annotated tags, create signed tags.

Also, explicitly specify the tag message.

Change-Id: If26601436df69cde5486444f9274b2f68c45d27b
diff --git a/Documentation/dev-release.txt b/Documentation/dev-release.txt
index ce89aa2..bd3c316 100644
--- a/Documentation/dev-release.txt
+++ b/Documentation/dev-release.txt
@@ -104,16 +104,16 @@
   ./tools/version.py 2.5
 ----
 
-Commit the changes and create the release tag on the new commit:
+Commit the changes and create a signed release tag on the new commit:
 
 ----
-  git tag -a v2.5
+  git tag -s -m "v2.5" v2.5
 ----
 
 Tag the plugins:
 
 ----
-  git submodule foreach git tag -a v2.5
+  git submodule foreach git tag -s -m "v2.5" v2.5
 ----
 
 [[build-gerrit]]