[DOC] Add Heroku install docs.
[DOC] Add Heroku install docs.

xdv/gatewayd,crazyquark/gatewayd,Parkjeahwan/awegeeks,whotooktwarden/gatewayd,zealord/gatewayd,xdv/gatewayd,Parkjeahwan/awegeeks,whotooktwarden/gatewayd,zealord/gatewayd,crazyquark/gatewayd