Improve documentation for contributors

[djmgit]

Documentations for contributors needs to be improved.

Presently only way to run Saberx mentioned in the doc is to run sudo python3 setup.py install
Running this command again and again while developing can prove to be tiring.

Saberx can be also run as a module using python3 -m saberx.driver.driver -f [config_file]
This needs to be mentioned in the doc.
So for development purpose, one can follow the following steps to run Saberx and test their
changes:

• sudo pip3 install -r requirements.txt
• hack, hack, hack...
• python3 -m saberx.driver.driver -f [config_file]

Also there needs to be doc for running tests, lint test and coverage.

Tests can be performed by simple running pytest from the root directory.
Lint test can performed by simply running flake8 from the root directory
Coverage can be determined by running pytest --cov=./ from the root directory

Lastly, while developing and adding new features or fixing bugs, one might want to keep it
separate from the global installation. This can be achieved by using any isolation tool, like
virtualenv. We also need doc on how to setup Saberx from within virtualenv.

All these things needs to be documented in CONTRIBUTING.md.