Update README.rst

[willianpaixao]

• Rosie link updated.
• Better explanation on creating virtual environments.
• Python commands replaced by Python3.

What is the purpose of this Pull Request? To have a more detailed and updated documentation for contribution.

What was done to achieve this purpose? Change the README.rst file.

How to test if it really works? Copy the commands and run locally.

Who can help reviewing it? Downloading the code and building it locally, following the tutorial.

[willianpaixao]

I just would like to better explain the reason why I requested the change from pythonand pip to python3and pip3. As Python 3 isn't the default in almost all OSes, the user must explicitly install and change the default in order to call Python 3 under the command python. [1]

More advanced users when facing the errors for building the code under Python 2.x would quickly understand and correct the commands but would be nice to make easier to use the more compatible command in the documentation.

[willianpaixao]

@cuducos changes regarding Python 3 reverted.

But I changed the codeto code-block blocks and now we have language code highlighted. :)

[cuducos]

But I changed the code to code-block blocks and now we have language code highlighted. :)

Yay 🎉

[willianpaixao]

All changes made and commits squashed.