build: manifest updates for extension submission

packages/app/README.md

@@ -4,6 +4,8 @@
 
 </div>
 
+Source code is available on Github at https://github.com/blockstack/ux/tree/master/packages/app
+
 The Blockstack App is an application for interacting and authenticating with [Blockstack](https://blockstack.org) apps. It can be used as a hosted web app (available at [app.blockstack.org](https://app.blockstack.org)) or as a browser extension.
 
 To use this application with your own Blockstack App, we recommend using [Blockstack Connect](https://github.com/blockstack/connect).

packages/app/src/manifest.json

@@ -10,7 +10,7 @@
   },
   "content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'",
   "permissions": [
-    "*://*/*"
+    "activeTab"
   ],
   "manifest_version": 2,
   "background": {