The "Usage Notes" section is often at the bottom of a long page of content
which can make it difficult to discover. This commit adds a link at the
end of the "Description" if there is a "Usage Notes" section on the page.
This link should help the reader to discover that there is more information
available further down the page.
This is basically a marginal fix. The longer term fix should be to
consider what content goes in which sections and how they should
be laid out on the page.
See #40753
PR Close#40835
