README: Add instructions for using a proxy server for Internet access.

Author: Akanksha Bhardwaj

README.rst

@@ -198,6 +198,10 @@ To access the vagrant server on a physical device:
 
     192.168.0.1:9991
 
+  Note that if you have internet access on your android device through
+  a proxy server, you might have to use a VPN application like `this
+  one`_ to connect to the server.
+
 | You can also route the IP address to a domain name like
   www.local.test.com (this routing is useful when testing the Google OAuth
   Backend)
@@ -213,6 +217,7 @@ If unclear you can follow tutorial here `Host Remapping`_
 
 .. _here: https://github.com/zulip/zulip/blob/1c40df9363b70af0e275c44a03f9627808852616/Vagrantfile#L37
 .. _Host Remapping: http://docs.telerik.com/fiddler/KnowledgeBase/HOSTS
+.. _this one: https://play.google.com/store/apps/details?id=com.psiphon3&hl=en
 .. _this: http://docs.telerik.com/fiddler/Configure-Fiddler/Tasks/ConfigureForAndroid