Create CONTRIBUTING.md

as it seems to be fashionable

CONTRIBUTING.md

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+## Welcome
+
+You may fork or even contribute under the Terms of the [License](./LICENSE.md).
+Some information on build and dependecies you will find in the [Readme](./README.md).
+
+Also have a look at other projects on [nek0's GitHub](https://github.com/nek0/).
+
+### Translation
+
+Some users already helped tranlating to their favorite languages, e.g.: English, German, Czech, French and Polish.
+
+If you can contribute another one, we are glad to include your translation along the other [language files](./messages/);
+please use UTF-8 as encoding for any special characters if possible.
+A flag or language indicating graphic file – preferably in a web compatible vector graphics format – is to be placed
+with [the images](./static/images).