add a/v calls to features

README.md

@@ -35,6 +35,7 @@
 
 * End-to-end encryption with [OMEMO](http://conversations.im/omemo/) or [OpenPGP](http://openpgp.org/about/)
 * Send and receive images as well as other kind of files
+* Make audio and video calls
 * Share your location
 * Send voice messages
 * Indication when your contact has read your message