Improvements in the README.rst

- > This is the official documentation for coala, and it is online at https://docs.coala.io. The coala repository can be found here.

It should be kept clear that the Documentation is in the coala repository. So the line should be
something like `The documentation resides in the coala repository which can be found here`

- > pip3 install -r requirements.txt

This command should be executed inside the coala folder, so, before this command, `cd coala` command should be added to make things more clear.