Update mobile testing docs

Update the documentation for testing the client on mobile devices
following the merge of https://github.com/hypothesis/h/pull/5758.

 - Remove the step involving changing the `CLIENT_URL` env var in the h
   dev environment

 - Add a Troubleshooting section

docs/developers/mobile.rst

@@ -13,7 +13,8 @@ tested with at least current versions of iOS Safari and Chrome for Android.
 
 #. Configure h to allow incoming connections from other systems
    by editing ``conf/development-app.ini`` and changing the ``host`` setting from
-   ``localhost`` to ``0.0.0.0``.
+   ``localhost`` to ``0.0.0.0``. You will need to restart the h dev server after
+   making this change.
 
 #. Get the hostname of your development system (``<HOSTNAME>``
    in the steps below). You can do this using the ``hostname`` terminal command on
@@ -28,24 +29,19 @@ tested with at least current versions of iOS Safari and Chrome for Android.
       accessible from other devices on the network. If you have problems using
       the hostname, try using the IP address instead.
 
-#. Set the :envvar:`CLIENT_URL` environment variable to configure h
-   to load the client from this host and start the dev server:
-
-   .. code-block:: sh
-
-      # In the h repository
+#. On your mobile device, go to a page which has the client embedded such as
+   ``http://<HOSTNAME>:3000`` or ``http://<HOSTNAME>:5000/docs/help``.
 
-      # Configure the URL that the client is loaded from in pages
-      # that embed Hypothesis
-      export CLIENT_URL=http://<HOSTNAME>:3001/hypothesis
+   These URLs will also work on your development system.
 
-      make dev
 
-#. Make sure the "Redirect URL" of the OAuth client associated with your
-   development client matches `<HOSTNAME>`. You can configure the OAuth clients
-   registered with h at http://localhost:5000/admin/oauthclients.
+Troubleshooting
+###############
 
-   This step is necessary to make logging into the client work.
+- If logging into the client does not work when the client is accessed via
+  a non-localhost URL, make sure the "Redirect URL" for the Hypothesis client's
+  "OAuth client" (managed at http://localhost:5000/admin/oauthclients) is
+  set to ``{current_scheme}://{current_host}:5000``.
 
-#. On your mobile device, go to a page which has the client embedded such as
-   ``http://<HOSTNAME>:3000`` or ``http://<HOSTNAME>:5000/docs/help``.
+- Make sure that you are not overriding the ``CLIENT_URL`` env var in your h
+  environment or ``SIDEBAR_APP_URL`` env var in your client dev environment