Add docs for MasterView.help_url and get_help_url()

docs/api/views/master.rst

@@ -68,10 +68,21 @@ override when defining your subclass.
       Factory callable to be used when creating new grid instances; defaults to
       :class:`tailbone.grids.Grid`.
 
-.. Methods to Override
+   .. attribute:: MasterView.help_url
-.. -------------------
+
-.. 
+      If set, this defines the "default" help URL for all views provided by the
-.. The following is a list of methods which you can override when defining your
+      master.  Default value for this is simply ``None`` which would mean the
-.. subclass.
+      Help button is not shown at all.  Note that the master may choose to
-.. 
+      override this for certain views, if so that should be done within
+      :meth:`get_help_url()`.
+
+
+Methods to Override
+-------------------
+
+The following is a list of methods which you can override when defining your
+subclass.
+
    .. .. automethod:: MasterView.get_settings
+
+   .. automethod:: MasterView.get_help_url

tailbone/views/master.py

@@ -107,6 +107,7 @@ class MasterView(View):
     use_index_links = False
 
     has_versions = False
+    help_url = None
 
     labels = {'uuid': "UUID"}
 
@@ -1693,7 +1694,18 @@ class MasterView(View):
         return self.request.route_url('{}.{}'.format(route_prefix, action), **kw)
 
     def get_help_url(self):
-        return getattr(self, 'help_url', None)
+        """
+        May return a "help URL" if applicable.  Default behavior is to simply
+        return the value of :attr:`help_url` (regardless of which view is in
+        effect), which in turn defaults to ``None``.  If an actual URL is
+        returned, then a Help button will be shown in the page header;
+        otherwise it is not shown.
+
+        This method is invoked whenever a template is rendered for a response,
+        so if you like you can return a different help URL depending on which
+        type of CRUD view is in effect, etc.
+        """
+        return self.help_url
 
     def render_to_response(self, template, data, mobile=False):
         """