Merge pull request rms-open-letter#891 from gasman/matthew-westcott

Add Matthew Westcott

Author: neilmcgovern

index.md

@@ -633,6 +633,7 @@ Signed,
 1. Matthew S. Wilson (former contributor GNU Image Manipulation Program and GNU Parted, former Director, Software Freedom Conservancy)
 1. Matthew Vernon (Debian developer)
 1. Matthew Venn
+1. Matthew Westcott (`gasman`, Wagtail CMS maintainer)
 1. Matthew Wilcox (Linux kernel hacker)
 1. Matthias Antierens
 1. Matthias Arnason