Use docs.opengrid.io to host documentation

[tomschenkjr]

We've been pointing to http://opengrid.readthedocs.io for documentation. However, this creates a different domain, which isn't great for someone who is wanting to discover the documentation. Instead, we can use docs.opengrid.io as an alternative domain.

Here are the documents for using CNAME with ReadTheDocs.

[tomschenkjr]

@reve0716 - can you login to ReadTheDocs and go to OpenGrid admin panel, click "Domains" and then insert http://docs.opengrid.io in Domain and check the "This Domain is the primary one where the documentation is served from."

This should enable the ReadTheDocs to be available at docs.opengrid.io.

After that is done, we'll do the following:

• We'll add a link on opengrid.io to point to this new URL on the main page.
• All the documentation, such as README.md and others should use docs.opengrid.io.