add changelogs/README.md

this is to quickstart contributors who don't work daily on the codebase

changelogs/README.md

+# Generating changelog entries
+
+To generate and validate your changelog entries:
+
+1. Run `bin/changelog` to generate.
+1. Run `scripts/lint-changelog-yaml` to validate.
+
+See [development/changelog] documentation for detailed usage.
+
+[development/changelog]: https://docs.gitlab.com/ee/development/changelog.html

changelogs/unreleased/changelogs-readme.yml

+---
+title: add readme to changelogs directory
+merge_request: 25209
+author: "@glensc"
+type: added

scripts/lint-changelog-yaml

@@ -3,7 +3,7 @@
 require 'yaml'
 
 invalid_changelogs = Dir['changelogs/**/*'].reject do |changelog|
-  next true if changelog =~ /(archive\.md|unreleased(-ee)?)$/
+  next true if changelog =~ /((README|archive)\.md|unreleased(-ee)?)$/
   next false unless changelog.end_with?('.yml')
 
   begin