[FAB-8698] - Fix broken link

Link to channel update tutorial is broken due to naming
change from 'channel_update' -> 'channel_update_tutorial'
[ci-skip]

Change-Id: I84bfbdc9fd0b86f359f45404f902b5deb67e80e8
Signed-off-by: Nick Gaski <nickgaski@gmail.com>

docs/source/capability_requirements.rst

@@ -77,7 +77,7 @@ reconfiguration).
 
 .. note:: We have a two documents that talk through different aspects of channel
           reconfigurations. First, we have a tutorial that will take you through
-          the process of :doc:`channel_update`. And we also have a document that
+          the process of :doc:`channel_update_tutorial`. And we also have a document that
           talks through :doc:`config_update` which gives an overview of the
           different kinds of updates that are possible as well as a fuller look
           at the signature process.