Add contributing docs

Author: matejchalk

README.md

@@ -118,3 +118,23 @@ This applies to file paths matching any of the following globs:
 - `**/fixtures/**/*.?(c|m)[jt]s?(x)`
 
 <!-- end autogenerated -->
+
+## 🫴 Contributing
+
+Node.js installation is a prerequisite (LTS version). Install dependencies with NPM:
+
+```sh
+npm install
+```
+
+To execute tests:
+
+```sh
+npm test
+```
+
+To generate documentation:
+
+```sh
+npm run docs
+```