API documentation in repo

[emeli-dral]

In addition to the existing documentation, we need to document the API.

Since such documentation is generated automatically, and the codebase is not entirely covered with comments, we shall do it step-by-step. As a first step, I suggest we:

• [ ] upload the first version of the automatically generated documentation
• [ ] upload the instructions for building the docs from the repository

This will allow us to:

1. see how the API documentation looks now and iteratively improve the content and visuals
2. give the users the opportunity to build it from the repository according to the instructions

[burkovae]

Any thoughts on what you want to use? shpinx? readthedocs?