Merge pull request #5916 from cylc/wxtim-patch-1

Update CONTRIBUTING.md

Author: wxtim

CONTRIBUTING.md

@@ -92,6 +92,7 @@ requests_).
  - John Haiducek
  - (Andrew Huang)
  - Cheng Da
+ - Mark Dawson
 <!-- end-shortlog -->
 
 (All contributors are identifiable with email addresses in the git version