per issue #312 replacing recommonmark with myst-parser

I have made things!

Checklist

• [x] I have double checked that there are no unrelated changes in this pull request (old patches, accidental config files, etc)
• [ ] I have created at least one test case for the changes I have made
• [ ] I have updated the documentation for the changes I have made
• [ ] I have added my changes to the CHANGELOG.md

Related issues

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@askalik please, see https://github.com/dry-python/returns/pull/1089 This is how it should be resolved.

Btw @sobolevn, don't forget to tag classes repo with hacktoberfest tag