Describe the usage of PhysiLearning in the docs

[sergiyayf]

For my code to be valuable it has to be reusable. Documentation is needed so people can read and understand how to use the code I wrote

[sergiyayf]

• [x] Created tree structure, updated index.rst and started filling in the meat. ToDo:
• [x] Write clearer and more thorough installation and getting started sections.
• [x] Fill in the code references sec
• [ ] Start writing the RL Algorithms

[sergiyayf]

Close this issue for better progress tracking