add my signature (rms-open-letter#16)

I first resigned from the FSF here https://anarc.at/blog/2019-09-16-fsf-resignations/

Co-authored-by: Elana Hashman <[email protected]>

Author: anarcat

index.md

@@ -50,3 +50,4 @@ Signed,
 - Jesse Cooke
 - Andrej Shadura
 - Amy Troschinetz
+- Antoine Beaupré AKA anarcat (Debian Developer, former FSF member)