[Bug-Minor] Documentation for API calls

[paulofer85]

Unity team found that:

1. we should check that documentation covers all API calls: Majority of public API methods are not covered in the documentation. Consider creating a separate documentation page dedicated solely for the C# API.
2. we should check that documentation is clear and contains no typos: Single-page documentation with setup, API and other details is difficult to follow and navigate
3. Check if public facing source code is summarized / commented

Actions to take:

1. Adding documentation and comments on methods (in .cs and .md files) .
2. Adding a single-page documentation for API calls (README-Api.md was added).
3. Have a separate documentation file for API Calls

[thebrianbug]

done