[3.0.x] Added missing backticks in various docs.

Backport of 30ca66e from master

docs/howto/custom-file-storage.txt

@@ -42,7 +42,7 @@ You'll need to follow these steps:
    ``django.utils.deconstruct.deconstructible`` class decorator for this
    (that's what Django uses on FileSystemStorage).
 
-By default, the following methods raise `NotImplementedError` and will
+By default, the following methods raise ``NotImplementedError`` and will
 typically have to be overridden:
 
 * :meth:`Storage.delete`
@@ -56,7 +56,7 @@ omitted. As it happens, it is possible to leave each method unimplemented and
 still have a working Storage.
 
 By way of example, if listing the contents of certain storage backends turns
-out to be expensive, you might decide not to implement `Storage.listdir`.
+out to be expensive, you might decide not to implement ``Storage.listdir()``.
 
 Another example would be a backend that only handles writing to files. In this
 case, you would not need to implement any of the above methods.

docs/internals/deprecation.txt

@@ -621,7 +621,7 @@ details on these changes.
 * Database test settings as independent entries in the database settings,
   prefixed by ``TEST_``, will no longer be supported.
 
-* The `cache_choices` option to :class:`~django.forms.ModelChoiceField` and
+* The ``cache_choices`` option to :class:`~django.forms.ModelChoiceField` and
   :class:`~django.forms.ModelMultipleChoiceField` will be removed.
 
 * The default value of the

docs/intro/reusable-apps.txt

@@ -169,7 +169,7 @@ this. For a small app like polls, this process isn't too difficult.
 
            path('polls/', include('polls.urls')),
 
-       3. Run `python manage.py migrate` to create the polls models.
+       3. Run ``python manage.py migrate`` to create the polls models.
 
        4. Start the development server and visit http://127.0.0.1:8000/admin/
           to create a poll (you'll need the Admin app enabled).

docs/ref/contrib/postgres/fields.txt

@@ -79,7 +79,7 @@ may be a good choice for the :ref:`range fields <range-fields>` and
 
 .. note::
 
-    When nesting ``ArrayField``, whether you use the `size` parameter or not,
+    When nesting ``ArrayField``, whether you use the ``size`` parameter or not,
     PostgreSQL requires that the arrays are rectangular::
 
         from django.contrib.postgres.fields import ArrayField

docs/ref/models/querysets.txt

@@ -498,7 +498,7 @@ Examples (those after the first will only work on PostgreSQL)::
 
     ...wouldn't work because the query would be ordered by ``blog__name`` thus
     mismatching the ``DISTINCT ON`` expression. You'd have to explicitly order
-    by the relation `_id` field (``blog_id`` in this case) or the referenced
+    by the relation ``_id`` field (``blog_id`` in this case) or the referenced
     one (``blog__pk``) to make sure both expressions match.
 
 ``values()``

docs/topics/forms/index.txt

@@ -355,7 +355,7 @@ from that ``{{ form }}`` by Django's template language.
     use the ``url``, ``email`` and ``number`` HTML5 input types. By default,
     browsers may apply their own validation on these fields, which may be
     stricter than Django's validation. If you would like to disable this
-    behavior, set the `novalidate` attribute on the ``form`` tag, or specify
+    behavior, set the ``novalidate`` attribute on the ``form`` tag, or specify
     a different widget on the field, like :class:`TextInput`.
 
 We now have a working web form, described by a Django :class:`Form`, processed