New Insiders section

[katharinalisalin]

Created a new and detailed Insiders section.

[squidfunk]

LGTM!

[alonsomoya]

I actually kind of miss the old view on what features are already in insider and the brilliant sponsorware approach taken with funding goals introduced in 🚀 The future of Material for MkDocs
It really helped having a view on exciting features coming next upstream, and an actual motivation to become insider

[squidfunk]

Thanks for your feedback! We're still sticking to the funding goal based approach – nothing changed. We just rearranged the information. It's now spread across multiple pages because the one single Insiders page became too big:

• Our story + why sponsorware
• Features and funding goals

We tried to answer all of the questions that we received again and again, and this made this step necessary.