update README for running tests against remote server

README.md

@@ -15,6 +15,13 @@ CaosDB project.
 - If you want to run just a single test, you can also select a single test file:  
   `pytest-3 tests/test_issues.py`
 
+## Run tests agains a remote caosdb server
+
+* There is a special mark `local_server`, which marks all test which cannot
+  pass when the server is not on the host where the test suite is running.
+* Start tests with `pytest -m "not local_server"` or
+  `tox -- -m "not local_server"`.
+
 # Further Reading
 
 Please refer to the [official gitlab repository of the CaosDB