doc: Update net/http notes. (#476)
doc: Update net/http notes. (#476)

Followup to #454. Mention that Fetch API can be used.

Mention that only net/http client is supported, server is not.

Also mention that by default, without third party polyfill modules for XHR or Fetch APIs, node.js will not support net/http.
gopherjs/gopherjs,albrow/gopherjs,albrow/gopherjs,albrow/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs