Update README.md

Remove inaccurate "Security Caveats" sentence, as discussed on the cordova-dev mailing list. 

For reference from http://en.wikipedia.org/wiki/Localhost#Name_resolution:
"The processing of any packets sent to a loopback address is implemented in the link layer of the TCP/IP stack. Such packets are never delivered to any network interface controller (NIC) or device driver".

Sorry about this @shazron and thanks @devgeeks.