Update Documentation to Add lessthan30() test and solution to slides

[aqsa505]

This issue depends on #356

Update the documentation to include the solution for the lessthan30() test in the Candy Kata slides.

Please note that this issue is created for GHC 2024 Open Source Day; thus, priority will be given to attendees of this event. After the event, this issue will be open to everyone.

[itsjenm]

Hello, I'm a GHC attended, submitted a pull request for #356 and would like to work on this issue next