doc: update compiler requirements in README
doc: update compiler requirements in README

The latest V8 upgrade and the C++11-ification of the source code in src/
requires a recent compiler.  Update the requirements in the README.

Fixes node-forward/node#35.

PR-URL: https://github.com/node-forward/node/pull/36
Reviewed-By: Fedor Indutny <e39d94bae70283f13d24c278e04952d6dad9384b@indutny.com>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node