Add link to PGO-WG 2019-03-28 status update.

Author: michaelwoerister

working-groups/pgo/NOTES.md

@@ -1,5 +1,6 @@
-#### *<p align="center">This WG hasn't had any meetings yet.</p>*
-
 # Profile-Guided Optimization Meeting Notes
 This document contains meeting notes from the PGO working group.
 
+
+## WG Status Update - 2019/03/28
+https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/weekly.20meeting.202019-03-28.20.2354818/near/161957622