chore: add CONTRIBUTING.md

Author: ace-of-aces

CONTRIBUTING.md

@@ -0,0 +1,52 @@
+# CONTRIBUTING
+
+Contributions are welcome, and are accepted via pull requests.
+Please review these guidelines before submitting any pull requests.
+
+## Process
+
+1. Fork the project
+1. Create a new branch
+1. Code, test, commit and push
+1. Open a pull request detailing your changes.
+
+## Guidelines
+
+* Please ensure the coding style running `composer lint`.
+* Send a coherent commit history, making sure each individual commit in your pull request is meaningful.
+* You may need to [rebase](https://git-scm.com/book/en/v2/Git-Branching-Rebasing) to avoid merge conflicts.
+* Please remember that we follow [SemVer](http://semver.org/).
+
+## Setup
+
+Clone your fork, then install the dev dependencies:
+```bash
+composer install
+```
+
+
+Build workbench:
+```bash
+composer build
+```
+
+## Playground
+
+You can visit a test application via [Workbench](https://github.com/orchestral/workbench):
+```bash
+composer serve
+```
+
+## Lint
+
+Lint your code:
+```bash
+composer lint
+```
+## Tests
+
+Run all tests:
+```bash
+composer test
+```
+

README.md

@@ -130,19 +130,13 @@ will be processed as:
 http://localhost:8000/image-transform/width=250,format=webp/example.jpg
 ```
 
-## Testing
-
-```bash
-composer test
-```
-
 ## Changelog
 
 Please see [CHANGELOG](CHANGELOG.md) for more information on what has changed recently.
 
 ## Contributing
 
-TODO
+Please see [CONTRIBUTING](CONTRIBUTING.md) for details.
 
 ## Credits