Add missing append in delayed best practices example

[beduncs]

Updated code block in delayed best practices docs

• added appending result to the results list before return in Break up computations into many pieces Do
• added appending result to the results list before return in Break up computations into many pieces Don't

[GPUtester]

Can one of the admins verify this patch?

[jrbourbeau]

Thanks @benjaminhduncan -- this is in

Also, I noticed this is your first code contribution to this repository. Welcome!