Add pkgtop project to README

[orhun]

[dcorbe]

Hello!

Thank you for contributing to termui. I've merged this PR into a downstream fork at https://github.com/dcorbe/termui-dpc

This was done in response to the following issue: #304 (comment)

My intention is not to create a permanent fork for termui. I'm only trying to facilitate maintenance while the original author(s) are away. My hope is that my fork is eventually merged back into this repo along with your commits.

I would like to invite you to collaborate further. I would appreciate any help curating fixes and generally getting this project going in the right direction. Thanks again for your contribution!