add CONTRIBUTING file

Author: huhn511

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+CONTRIBUTING ON NILE
+============
+
+There are three ways in which you can contribute to the nile project:
+
+1. By improving the documentation or [specification](https://github.com/nileorg/nile-specifications).
+2. By solving an issue of our code basis issue lists.
+ 1. [instance  issue list](https://github.com/nileorg/nile-local-instance/issues)
+ 2. [node issue list](https://www.nile.shopping) (soon)
+ 2. [client issue list](https://www.nile.shopping) (soon)
+3. By testing the application and report bugs or suggestions.
+
+Choosing what to work on in a large open source project is not easy. The general list of issues can you find here: [Nile general issue list](https://github.com/nileorg/nile-development/issues).
+
+
+## General
+- If something is unclear for you, you can ask anything in the #development channel in [our Discord server](https://discord.gg/eZFan9).
+
+
+## Development
+
+- Create a merge request and describe your intention for the changes.
+- The test suites and linters must pass. More information about this you will find in the README.md files of each repository.
+- Verify that your changes work ;-)
+
+## Documentation
+
+- No spelling mistakes
+- No orthographic mistakes
+- No Markdown syntax errors