My first HTML5 page - 1 warning - no details

Having spent many years hand coding HTML 4.1 I decided to see if I could
convert to HTML5

After editing out all the errors initially reported by your Validator
service, I was left with just 1 warning - but no details

I have double checked as best I can (being new to HTML5) 

Please advise if possible?

Here is my "new" file

http://grumpyoldgits.org/chums/5dicky.htm

Many thanks!

Richard Nourse
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