Update docs for self-hosted runners

docs/source/developer_guide/ci.rst

@@ -0,0 +1,29 @@
+======================
+Continuous Integration
+======================
+
+General instructions for setting up self-hosted GitHub runners can be found `here <https://docs.github.com/en/actions/hosting-your-own-runners>`_.
+
+This process typically involves:
+
+1. Add a new self-hosted runner on GitHub
+2. Run instructions from GitHub on your runner to download and configure
+3. Ensure tags added to the runner are unique, and match those in ``runs-on`` within the CI workflow
+
+
+MacOS self-hosted runner
+========================
+
+Currently, ``janus-core`` uses a self-hosted runner to run all unit tests on MacOS.
+
+To ensure the self-hosted runner remains active, we currently recommend using
+
+.. code-block:: bash
+
+    nohup ./run.sh &!
+
+This runs the script in the background, and disowns the process, allowing the ssh connection to be ended without killing the process.
+
+It would be preferable to `configure the runner application as a service <https://docs.github.com/en/actions/hosting-your-own-runners/managing-self-hosted-runners/configuring-the-self-hosted-runner-application-as-a-service?platform=mac>`_,
+but currently this appears to lead to difficulties if the GUI is not active
+and/or ``sudo`` permissions are not used in running the service.

docs/source/developer_guide/index.rst

@@ -7,3 +7,4 @@ Developer guide
 
     get_started
     tutorial
+    ci