docs: add note about baseURL and debug toolbar

Author: kenjis

user_guide_src/source/installation/running.rst

@@ -21,6 +21,11 @@ Initial Configuration
    set your base URL to ``$baseURL``. If you need more flexibility, the baseURL may
    be set within the **.env** file as ``app.baseURL = 'http://example.com/'``.
    (Always use a trailing slash on your base URL!)
+
+    .. note:: If you don't set the ``baseURL`` correctly, in development mode,
+        the debug toolbar may not load properly and web pages may take considerably
+        longer to display.
+
 #. If you intend to use a database, open the
    **app/Config/Database.php** file with a text editor and set your
    database settings. Alternately, these could be set in your **.env** file.