Mention the target audience

[xiazeyu]

Could you please mention the target audience both in README and the paper.

Thank you!

Ref openjournals/joss-reviews#8680

[xiazeyu]

Sorry. I found that at the end of the documentation. https://forefire.readthedocs.io/en/latest/about/statement_of_need.html

[xiazeyu]

Recommended promotion to a more prominent position