Add links to the wiki

README.md

 # Bramble specification
 
+The wiki has an explanatory [overview of the protocol stack](https://code.briarproject.org/briar/briar/wikis/A-Quick-Overview-of-the-Protocol-Stack)
+as well as text on
+[the architecture](https://code.briarproject.org/briar/briar/wikis/home#architecture).
+
+## Formal specifications in this repo
+
 - [Binary Data Format](BDF.md)
 - [Bramble Handshake Protocol](protocols/BHP.md)
 - [Bramble QR Code Protocol](protocols/BQP.md)