Link to online documentation

[graemenelson]

It might be helpful for others who are new to Kibana 3 to have a link to online documentation on the README page. I know there's the asciidoc, but I was new to them and it took me a while to figure out how to build an html5 version.

Cheers.

[kkirsche]

This issue is fixed by https://github.com/elastic/kibana/blob/master/README.md#documentation

[tbragin]

Closing as fixed.