Merge pull request #3 from vojtech-dobes/polish

Add GitHub Actions badge to readme

Author: vojtech-dobes

docs/readme.md

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 # 📓 Grammar Processing for PHP
 
+![Checks](https://github.com/vojtech-dobes/php-grammar-processing/actions/workflows/checks.yml/badge.svg?branch=master&event=push)
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 This library provides convenient APIs for describing a context-free grammar, and subsequently using it to build an abstract syntax tree and analyze it for an arbitrary purpose.