docs: deprecate github documentation in favor of the website

[dkrutskikh]

What is the purpose of this pull request? (put an "X" next to an item)

[X] Documentation update
[ ] Bug fix
[ ] New rule
[ ] Changes an existing rule
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

Is there anything you'd like reviewers to focus on?

[codecov]

Codecov Report

Merging #498 (d266eb0) into master (e93a56f) will not change coverage.
The diff coverage is n/a.

❗ Current head d266eb0 differs from pull request most recent head 0db56aa. Consider uploading reports for the commit 0db56aa to get more accurate results

@@           Coverage Diff           @@
##           master     #498   +/-   ##
=======================================
  Coverage   84.10%   84.10%           
=======================================
  Files         205      205           
  Lines        4229     4229           
=======================================
  Hits         3557     3557           
  Misses        672      672           

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