ENH: added section on continuous integration

> There’s no discussion of using web hooks here — does save do that, or…?
> This isn’t the way I use binstar-build, so its new to me and I’m a little confused.
> Why would I use the binstar-build CLI in place of web hooks?

I have just added the docs for using web hooks. The exampels in the docs should be looked at as a progression to get to using the web hooks.

cc @tswicegood

@lilahickey can you review?