create contributing guide

CONTRIBUTING.md

@@ -0,0 +1,43 @@
+# Contributing to PHP-ML
+
+PHP-ML is an open source project. If you'd like to contribute, please read the following text. Before I can merge your 
+Pull-Request here are some guidelines that you need to follow. These guidelines exist not to annoy you, but to keep the 
+code base clean, unified and future proof.
+
+## Branch
+
+You should only open pull requests against the develop branch.
+
+## Unit-Tests
+
+Please try to add a test for your pull-request. You can run the unit-tests by calling:
+
+```
+bin/phpunit
+```
+
+## Travis
+
+GitHub automatically run your pull request through Travis CI against PHP 7. 
+If you break the tests, I cannot merge your code, so please make sure that your code is working 
+before opening up a Pull-Request.
+
+## Merge
+
+Please allow me time to review your pull requests. I will give my best to review everything as fast as possible, but cannot always live up to my own expectations.
+
+## Coding Standards
+
+When contributing code to PHP-ML, you must follow its coding standards. To make a long story short, here is the golden tool:
+
+```
+tools/php-cs-fixer.sh
+```
+
+This script run PHP Coding Standards Fixer with `--level=symfony` param.
+
+More about PHP-CS-Fixer: [http://cs.sensiolabs.org/](http://cs.sensiolabs.org/)
+
+---
+
+Thank you very much again for your contribution!

README.md

@@ -84,17 +84,12 @@ Example scripts are available in a separate repository [php-ai/php-ml-examples](
     * [Matrix](http://php-ml.readthedocs.io/en/latest/math/matrix/)
     * [Statistic](http://php-ml.readthedocs.io/en/latest/math/statistic/)
 
-
 ## Contribute
 
 - Issue Tracker: github.com/php-ai/php-ml/issues
 - Source Code: github.com/php-ai/php-ml
 
-After installation, you can launch the test suite in project root directory (you will need to install dev requirements with Composer)
-
-```
-bin/phpunit
-```
+You can find more about contributing in [CONTRIBUTING.md](CONTRIBUTING.md).
 
 ## License
 

docs/index.md

@@ -90,11 +90,7 @@ Example scripts are available in a separate repository [php-ai/php-ml-examples](
 - Issue Tracker: github.com/php-ai/php-ml/issues
 - Source Code: github.com/php-ai/php-ml
 
-After installation, you can launch the test suite in project root directory (you will need to install dev requirements with Composer)
-
-```
-bin/phpunit
-```
+You can find more about contributing in [CONTRIBUTING.md](CONTRIBUTING.md).
 
 ## License