docs(README): add usage section

Author: paulschwoerer

README.md

@@ -1,3 +1,10 @@
 # sipgate Python E2E-Test Utils
 
 This is a Python library for common utils used in sipgate-specific E2E testing (XML-, JSON-RPC, awaiting assertions, JobD helpers).
+
+## Usage
+In order to include this module in your project, add e.g.
+
+`sipgate_e2e_test_utils @ git+https://github.com/sipgates/sipgate-e2e-test-utils.git@main`
+
+to your `requirements.txt`.