Fix remaining sphinx warnings

Author: mwcraig

.readthedocs-requirements.txt

@@ -0,0 +1,6 @@
+.. _aida_backends:
+
+AIDA Backends
+=============
+
+The following packages implement the Astronomical Image Display API (AIDA):

docs/_static/favicon.ico

@@ -15,7 +15,7 @@ want to write a package that displays astronomical images and provide a
 uniform interface for users to interact with these images programmatically.
 
 If you are a user looking for a way to display astronomical images, please
-see the `aida-backends`_ page, which has a list of packages that implement
+see the :ref:`aida_backends` page, which has a list of packages that implement
 this API.
 
 How to implement this API in your package
@@ -35,3 +35,12 @@ How to implement this API in your package
    of image and catalog labels. You are **not** required to use this reference
    implementation; it is just a convenience you can use to get started if you
    want to.
+
+.. toctree::
+  :maxdepth: 1
+  :hidden:
+
+  api.rst
+  reference_implementation.rst
+  testing_implementation.rst
+  aida_backends.rst

docs/aida_backends.rst

@@ -494,7 +494,7 @@ def get_viewport(
             - 'image_label' is a string representing the label of the image.
 
         Raises
-        -------
+        ------
         ValueError
             If the `sky_or_pixel` parameter is not one of 'sky', 'pixel', or `None`,
             or if the `image_label` is not provided when there are multiple images