[docs] add contribution doc.

Author: makasim

docs/contribution.md

@@ -0,0 +1,29 @@
+# Contribution
+
+To contribute you have to fork a [enqueue-dev](https://github.com/php-enqueue/enqueue-dev) repository.
+Clone it locally.
+ 
+## Setup environment
+
+```
+composer install
+./bin/pre-commit -i
+./bin/dev -b
+```
+
+Once you did it you can work on a feature or bug fix.
+
+## Testing
+
+To run tests simply run 
+
+```
+./bin/dev -t
+```
+
+## Commit 
+
+When you try to commit changes `php-cs-fixer` is run. It fixes all coding style issues. Dont forget to stage them and commit everything.
+Once everything is done open a pull request on official repository. 
+
+[back to index](index.md)

docs/index.md

@@ -22,4 +22,7 @@
     - [Consumption extension](bundle/consumption_extension.md)
     - [Production settings](bundle/production_settings.md)
     - [Debuging](bundle/debuging.md)
-    - [Functional testing](bundle/functional_testing.md)
+    - [Functional testing](bundle/functional_testing.md)
+* Development
+    - [Contribution](contribution.md)
+