bug 1218563: Update documentation doc for Docker
bug 1218563: Update documentation doc for Docker

Re-write the documentation for updating the documentation to use Docker.
A virtualenv in the host machine is still the fastest way to generate
documentation, but a method is given for using Docker, which may more
practical in the future.

safwanrahman/kuma,jwhitlock/kuma,safwanrahman/kuma,ollie314/kuma,ollie314/kuma,yfdyh000/kuma,SphinxKnight/kuma,a2sheppy/kuma,safwanrahman/kuma,ollie314/kuma,jwhitlock/kuma,mozilla/kuma,mozilla/kuma,jwhitlock/kuma,safwanrahman/kuma,mozilla/kuma,jwhitlock/kuma,SphinxKnight/kuma,a2sheppy/kuma,mozilla/kuma,yfdyh000/kuma,yfdyh000/kuma,ollie314/kuma,escattone/kuma,Elchi3/kuma,SphinxKnight/kuma,a2sheppy/kuma,mozilla/kuma,safwanrahman/kuma,SphinxKnight/kuma,Elchi3/kuma,Elchi3/kuma,SphinxKnight/kuma,escattone/kuma,yfdyh000/kuma,SphinxKnight/kuma,Elchi3/kuma,safwanrahman/kuma,a2sheppy/kuma,yfdyh000/kuma,escattone/kuma,ollie314/kuma,Elchi3/kuma,jwhitlock/kuma,yfdyh000/kuma,a2sheppy/kuma,ollie314/kuma