Added contribution guidelines

README.md

@@ -54,6 +54,10 @@ Ask for help or report issues:
 4. Open `<XenkoDir>\samples\XenkoSamples.sln` and play with the samples.
 5. Optionally, open and build `Xenko.Android.sln`, `Xenko.iOS.sln`, etc...
 
+### Contribution Guidelines
+
+Please check our [Contributing Guidelines](docs/CONTRIBUTING.md).
+
 ### Build Status
 
 |Branch| **master** |

docs/CONTRIBUTING.md

@@ -0,0 +1,18 @@
+# Contributing to Xenko
+
+## Check our issue tracker
+
+Please take a look at our [issue tracker](https://github.com/xenko3d/xenko/issues), especially issues marked with [help wanted](https://github.com/xenko3d/xenko/labels/help%20wanted).
+
+If you are just getting started with Xenko, issues marked with [good first issue](https://github.com/xenko3d/xenko/labels/good%20first%20issue) can be a good entry point.
+
+## Let other people know what you are doing
+
+Once you work on some task, notify people on the appropriate issue (create one if none exists) to:
+* make sure that no two people waste time doing the same thing
+* lay out your plans and discuss it with collaborators to make sure it is properly architectured and would fit well in the project
+* get feedbacks from other people
+
+## Coding style
+
+There's no Coding Style spec yet (and it will properly be done through a StyleCop & editorconfig file), but in the meantime please follow the coding style of other Xenko files.