[TM-410] Indigo website

Description

Transform the existing Indigo tutorial to a website.

The website can be statically built with mkdocs and is a customized version of most readthedocs websites.

Note: mkdocs is used strictly, meaning warnings will fail the build, including for reasons related to the included python-markdown module (e.g. an example source file has been moved). Also, this failing has been checked on CI as well.

Related issue(s)

https://issues.serokell.io/issue/TM-410

✅ Checklist for your Merge Request

Related changes (conditional)

• Tests (see short guidelines)

  • If I added new functionality, I added tests covering it.
  • If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • I checked whether I should update the docs and did so if necessary:
    • Root README and other README.md files
    • Haddock
    • docs/
  • I updated changelog files of all affected packages released to Hackage if my changes are externally visible.

Stylistic guide (mandatory)

• My commits comply with the following policy.
• My code complies with the style guide.