First draft of the contribution guidelines

CONTRIBUTING.md

@@ -1 +1,37 @@
+# Contribution Guidelines
+
+## Auto-Formatting
+ECL uses clang-format to auto-format the code. Currently it is using the clang-format-6.0.
+The enforced style is based on the google style. Google's [Style Guide](https://google.github.io/styleguide/cppguide.html) is the place to look for advice.
+The format is not enforced on all files. The list of files on which the auto-format checks are run on can be found in `tools/format.sh`
+
+On Ubuntu (tested on 18.04) the following command can be used to check if the code is complying with the format requirements
+```
+make check_format
+```
+To auto-format the code run
+```
+make format
+```
+
+## Continuous Integration
+There are multiple checks run on a submitted PR:
+
+| Test  | Description |
+| ------------- | ------------- |
+| - **Build tests**         | Checks if the submitted code is building on various platforms. |
+| - **Unit tests**          | Run checks if the code is satisfying test cases in `tests/` and report code coverage. |
+| - **Format checks**       | Check if the files specified in `/tools/format.sh` match the style specified in `.clang-format`. Run [auto-formatting](#Auto-Formatting) |
+| - **Firmware build tests**| Loads current `PX4/Firmware/master` and checks if ECL compiles with it. This test can fail if you change the ECL interface.As this can be necessary from time to time, this test is not required for | merging. But keep in mind to adapt the interface in `PX4/Firmware`
+
+## Unit tests
+# How to run the tests
+The test can be executed by running:
+```
+make test
+```
+
+# How to add a test
+tbd
+