Set MTU for device

The code tries setting the interface 'up' and 'running'. Setting the MTU may be required to get it running.
Set to a more widely used value
Fix various grammar mistakes and wording on README
Merge branch 'patch-1' of https://github.com/descention/cjdns
Merge branch 'master' of https://github.com/cjdelisle/cjdns
Android: Some touchups to the README in response to Finn's recommendations