Small addition to "apache-proxy"

[Nicholas]

Hi all,

I'm new to mod_rewrite and forgot to enable mod_proxy when deploying my
CherryPy app. On Apache 2, this manifests as 404 errors. It might save
someone a few minutes if there was a note in the documentation about
this, here:

http://docs.cherrypy.org/apache-proxy

The page does already suggests enabling mod_proxy, but only in response
to "Permission denied" errors, not 404s.

Currrent paragraph:

If you get Forbidden - You don't have permission to access / on this
server errors, try enabling the proxy module.

Proposed new paragraph:

If you get "Page not found" or "Forbidden - You don't have permission
to access / on this server" errors, try enabling the proxy module.

Thanks for the great documentation otherwise. The best part about
CherryPy though is that for the most part I didn't need it.