[skip ci] add contributing

Author: selul

CONTRIBUTING.md

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+## Releasing
+
+This repository uses conventional [changelog commit](https://github.com/Codeinwp/conventional-changelog-simple-preset) messages to trigger release
+
+How to release a new version:
+
+- Clone the master branch
+- Do your changes
+- Send a PR to master and merge it using the following subject message
+    - `release: <release short description>` - for patch release
+    - `release(minor): <release short description>` - for minor release
+    - `release(major): <release short description>` - for major release
+      The release notes will inherit the body of the commit message which triggered the release. For more details check the [simple-preset](https://github.com/Codeinwp/conventional-changelog-simple-preset) that we use.