Number entry: add an input hint "Write your answer as a fraction", shown when "must be reduced" is false

[carlortiz]

Hi @christianp!

Happy holidays! I would like to help out with this issue.

I've made changes and attempted to make a pull request. However, I was denied permission.

Here are screenshots of the changes I've made. Please let me know if I did something wrong, or you would like more information. Thank you!

Screenshots:

[christianp]

@carlortiz thanks for offering to help. I think you need to fork the Numbas repository before you can create a pull request. There's a page in the GitHub docs explaining what to do.