[3.1.x] Added backticks to code literals in various docs.

Backport of 550297d20d from master

docs/ref/forms/fields.txt

@@ -1323,7 +1323,7 @@ generating choices. See :ref:`iterating-relationship-choices` for details.
 .. class:: ModelMultipleChoiceField(**kwargs)
 
     * Default widget: :class:`SelectMultiple`
-    * Empty value: An empty ``QuerySet`` (self.queryset.none())
+    * Empty value: An empty ``QuerySet`` (``self.queryset.none()``)
     * Normalizes to: A ``QuerySet`` of model instances.
     * Validates that every id in the given list of values exists in the
       queryset.

docs/ref/models/instances.txt

@@ -568,7 +568,7 @@ all of the model fields from being updated in the database. For example::
     product.save(update_fields=['name'])
 
 The ``update_fields`` argument can be any iterable containing strings. An
-empty ``update_fields`` iterable will skip the save. A value of None will
+empty ``update_fields`` iterable will skip the save. A value of ``None`` will
 perform an update on all fields.
 
 Specifying ``update_fields`` will force an update.

docs/ref/models/querysets.txt

@@ -814,8 +814,8 @@ ambiguous datetimes in daylight saving time. By default (when ``is_dst=None``),
 
 .. method:: none()
 
-Calling none() will create a queryset that never returns any objects and no
+Calling ``none()`` will create a queryset that never returns any objects and no
-query will be executed when accessing the results. A qs.none() queryset
+query will be executed when accessing the results. A ``qs.none()`` queryset
 is an instance of ``EmptyQuerySet``.
 
 Examples::

docs/releases/1.7.txt

@@ -127,7 +127,8 @@ composite keys in future releases of Django, the
 
 This method takes no arguments, and returns a tuple of four items:
 
-* ``name``: The field's attribute name on its parent model, or None if it is not part of a model
+* ``name``: The field's attribute name on its parent model, or ``None`` if it
+  is not part of a model
 * ``path``: A dotted, Python path to the class of this field, including the class name.
 * ``args``: Positional arguments, as a list
 * ``kwargs``: Keyword arguments, as a dict

docs/topics/checks.txt

@@ -47,9 +47,9 @@ check function::
         return errors
 
 The check function *must* accept an ``app_configs`` argument; this argument is
-the list of applications that should be inspected. If None, the check must be
+the list of applications that should be inspected. If ``None``, the check must
-run on *all* installed apps in the project. The ``**kwargs`` argument is required
+be run on *all* installed apps in the project. The ``**kwargs`` argument is
-for future expansion.
+required for future expansion.
 
 Messages
 --------

docs/topics/db/queries.txt

@@ -1224,7 +1224,8 @@ Things get more complicated if you use inheritance. Consider a subclass of
     django_blog = ThemeBlog(name='Django', tagline='Django is easy', theme='python')
     django_blog.save() # django_blog.pk == 3
 
-Due to how inheritance works, you have to set both ``pk`` and ``id`` to None::
+Due to how inheritance works, you have to set both ``pk`` and ``id`` to
+``None``::
 
     django_blog.pk = None
     django_blog.id = None