Link handbook from deprecation template

data/deprecations/templates/example.yml

@@ -6,7 +6,7 @@
 # and what types we expect those attribute values to be.
 #
 # For more information please refer to the handbook documentation here:
-# {{LINK TBD}}
+# https://about.gitlab.com/handbook/marketing/blog/release-posts/#deprecations
 #
 # Please delete this line and above before submitting your merge request.