Improve the documentation

[pawel-czyz]

There's room for improvement for documentation:

• [ ] Add a picture of the benchmark to the ReadMe/docs.
• [x] Explicitly list estimators and cite their resources (See #135). Some ideas:
  • Add estimator.cite() method.
  • Add the citations to the documentation (e.g., to the webpage listing the existing estimators by including them in the docstrings).

Additionally, the following tutorial sections in documentation would be useful to add:

• [ ] How to use the samplers
• [ ] How to use the tasks.
• [x] How to use the estimators. (See #135)
• [x] How to add a new estimator. (See #134, #135)
• [x] How to define and use the fine distributions. (See #138)
• [ ] How to use Snakemake workflows.

A possible suggestion how to structure things: https://omnibenchmark.org/