Add Derek Schuff and Heejin Ahn as WebAssembly backend maintainers (#156553)

Co-authored-by: Nikita Popov <[email protected]>

Author: dschuff

llvm/Maintainers.md

@@ -312,6 +312,11 @@ [email protected] (email), [kaz7](https://github.com/kaz7) (GitHub)
 
 #### WebAssembly backend
 
+Derek Schuff \
+[email protected] (email), [dschuff](https://github.com/dschuff) (GitHub) \
+Heejin Ahn \
+[email protected] (email), [aheejin](https://github.com/aheejin) (GitHub)
+
 #### X86 backend
 
 Simon Pilgrim \