Modify docs.voltha.org

Docs for VOLTHA can be found on the website or via web search:

Browse repository content:

Checkout, modify and test:

$ git clone ssh://gerrit.opencord.org:29418/voltha-docs

$ cd voltha-docs
$ vi *.rst
$ make html           # doc generation
$ make test           # syntax check *.rst files

$ "$BROWSER" _build/html/index.html  # BROWSER='firefox'