docs: add CONTRIBUTING.md

Author: kulti

CONTRIBUTING.md

@@ -0,0 +1,19 @@
+# :construction: Contributing to Enapter UCM Lua Libraries
+
+Feel free to:
+
+- 🐛 Report an issue
+- 📖 Improve documentation
+- 👨‍💻 Contribute to the code
+
+## Creating a New Release
+
+A new release should be generated by the following command:
+```sh
+./tools/new_release.sh X.Y.Z
+```
+
+It generates new rockspec and updates the changelog. Please review the changes and commit it with:
+```sh
+git commit -m "release: vX.Y.Z"
+```