Index includes readme

At https://github.com/writethedocs/docs/tree/e9b4482a9c8496d4d203841d04739c8846dd5df5 the `.. include:: index.rst` is wrong: should be `docs/index.rst`.

Fixed with https://github.com/benoitbryon/docs.writethedocs/commit/e4d57a61627c186bffc5083e3ffca812f609e4ee

But, the `.. include::` still doesn't work as expected with Github RST parser: [nothing is displayed] (https://github.com/benoitbryon/docs.writethedocs/tree/e4d57a61627c186bffc5083e3ffca812f609e4ee)

[This pull request proposes a fix where docs/index includes readme] (https://github.com/benoitbryon/docs.writethedocs/tree/87224f80139dd8a9131819333d6e73788145c511).

The README has also been modified: added links to project's resources. So that the README becomes an entry point for the project. When one comes to writethedocs on Github, he gets a summary of the project, and quick links to project's resources, i.e. have the opportunity to continue at the right location.

docs/index includes README, so...

* don't repeat README. README is the document to maintain.
* docs/index also provides quick links to project's resources.