Add Proxy-Wasm update to 4/22 agenda.

Author: PiotrSikora

meetings/2021/WASI-04-22.md

@@ -28,4 +28,5 @@ The meeting will be on a zoom.us video conference.
 1. Announcements
     1. _Sumbit a PR to add your announcement here_
 1. Proposals and discussions
+    1. [Proxy-Wasm](https://github.com/proxy-wasm) update (Piotr Sikora)
     1. _Sumbit a PR to add your agenda item here_