Configure GitHub Actions

[Gr1N]

Need to configure GitHub Actions.

What we expect:

• configured markdown linter;
• configured zsh linter (maybe https://github.com/zdharma/zsh-lint);
• updated README.md with badges and related information.

Useful links:

• https://help.github.com/en/actions/automating-your-workflow-with-github-actions

[Gr1N]

To decide:

• https://github.com/koalaman/shellcheck
• https://github.com/mvdan/sh

[Gr1N]

More useful links:

• https://github.com/actions/toolkit