fix image URLs in the RSS feed.

Author: FoamyGuy

_includes/downloads/board_image.html

@@ -1,7 +1,7 @@
   {% assign small_image = "/assets/images/boards/small/" | append: include.board_image %}
   {% assign large_image = "/assets/images/boards/large/" | append: include.board_image %}
-  <img srcset="{{ small_image }} 300w,
-               {{ large_image }} 700w"
+  <img srcset="https://circuitpython.org{{ small_image }} 300w,
+               https://circuitpython.org{{ large_image }} 700w"
        sizes="(max-width: 1024px) 700px,
               300px"
-       src="{{ large_image }}" alt="Image of Board" loading="lazy">
+       src="https://circuitpython.org{{ large_image }}" alt="Image of Board" loading="lazy">