feat: added default fallback image for Card.ImageCap component (#12)

Author: peterkulko

README.rst

@@ -49,4 +49,10 @@ Files this package must make available
     :alt: favicon
     :width: 32px
 
+``/paragon/images/card-imagecap-fallback.png`` A variant of the default fallback image for `Card.ImageCap` component.
+
+.. image:: /paragon/images/card-imagecap-fallback.png
+    :alt: card-imagecap-fallback
+    :width: 380px
+
 ``/paragon/fonts.scss``, ``/paragon/_variables.scss``, ``/paragon/_overrides.scss``  A SASS theme for `@edx/paragon <https://github.com/openedx/paragon>`_. Theming documentation in Paragon is coming soon. In the meantime, you can start a theme by the contents of `_variables.scss (after line 7) <https://github.com/openedx/paragon/blob/master/scss/core/_variables.scss#L7-L1046>`_ file from the Paragon repository into this file.