Update charter with communication responsibilities

It has been brought up in
nodejs/admin#977 (comment).

Signed-off-by: Darshan Sen <raisinten@gmail.com>
Co-authored-by: Joyee Cheung <joyeec9h3@gmail.com>

Author: RaisinTen

TSC-Charter.md

@@ -74,6 +74,7 @@ including:
 * Development process and any coding standards.
 * Mediating technical conflicts between Collaborators or Foundation
   projects.
+* Technical communication.
 
 The TSC will define Node.js project’s release vehicles.