Add nimble.css

[Leftium]

Add: https://github.com/Leftium/nimble.css

It's new, but I've integrated into 9 of my actively maintained projects, including:

• A project I've maintained and used daily for over 3 years: https://github.com/Leftium/multi-launch
• Personal web site: https://github.com/Leftium/leftium.com

[dbohdan]

Promising, but I am not going to add a brand-new project like this. Please ping me if your project is maintained in six months. I'll keep the issue open.