Update mkdocs.yml

Adding IO-rev-6 docs

Author: wl-estensd

mkdocs.yml

@@ -171,6 +171,7 @@ nav:
 
   - I/O interface cards: 
       - Revision 4: io-interface-cards/io-interface-rev4.md
+      - Revision 6: io-interface-cards/io-interface-rev6.md
 
 
 copyright: © Water Linked 2018-2026