Update readthedocs to have an overview and tutorial sections

[rgerkin]

Currently it is just API docs, and the overview and tutorials are distributed through GitHub and the project site. They should also appear in the readthedocs site with the auto-generated API documentation. Several .rst files will need to be created.
@ChihweiLHBird

[ChihweiLHBird]

Can they (.rst files) be automatically generated by sphinx? Or I should create them manually?

[rgerkin]

These will need to be created manually (or from a tool that converts markdown files (.md) or html to .rst). Some good starting point for the source material would be:

• The README.md at the root of this repository
• The html output of any of the notebooks in the /docs directory of this repository
• The content of http://sciunit.io/sciunit.html
  If one or more of the above could be at the main page of the docs at http://sciunit.readthedocs.io that would be great. Right now it is just an index with auto-generated API documentation.

[ChihweiLHBird]

These will need to be created manually (or from a tool that converts markdown files (.md) or html to .rst). Some good starting point for the source material would be:

• The README.md at the root of this repository
• The html output of any of the notebooks in the /docs directory of this repository
• The content of http://sciunit.io/sciunit.html
  If one or more of the above could be at the main page of the docs at http://sciunit.readthedocs.io that would be great. Right now it is just an index with auto-generated API documentation.

Great, let me see how can I work on this.

[ChihweiLHBird]

Readme was added to index.rst. A pull request for it was created.

[ChihweiLHBird]

Fixed in 57c6742