Update nginx config file examples + README

Related to Pull Request #143 and https://github.com/dotcloud/docker/issues/1486.

This updates the config examples and documentation surrounding nginx configuration and chunked transfers.  Versions greater than 1.3.9 of nginx now support the chunked_transfer_encoding [directive][1].  The HttpChunkinModule is now in maintenance mode because of the [added support][2].

Merely adding the chunked_transfer_encoding directive on versions greater than 1.3.9 resolves the 411 HTTP error.  The lessens requirements and the PITA factor for new nginx installs with the registry.

[1]: http://wiki.nginx.org/HttpCoreModule#chunked_transfer_encoding
[2]: http://wiki.nginx.org/HttpChunkinModule#Status