Add integration test documentation

Author: SimonBaeumer

docs/development.md

@@ -0,0 +1,13 @@
+# Development documentation
+
+## Writing integration tests
+
+Commander tests itself. You can find the integration tests in `commander_unix.yaml` and `commander_windows.yaml`.
+More complex scenarios are stored in `integration/`.
+
+It is always necessary to execute the test suite with a stable version of commander and not the current build.
+
+**Tipps:**
+
+ - The working directory is by default the project root, even for tests located inside `integration/*`
+ - Execute `commander` inside the `commander_*.yaml` files with a given suite and assert the result which is returned