Functions-samples: docs(readme): add a Table Of Contents or create a Minisite

[adamlaz]

Summary

• It would be great to have a simple Table of Contents at the top of the README.md.
  _* Numbered list w/ Titles_
• It'd be even better to have a static site with better ux than readme.md.
  _* Titles & Descriptions_
  _* Screenshots_
  _* Tags and/or Categories_

Why?

There are quite a few cloud functions now and it's hard to know what is in here without following the repo activity or spending time+ to grok.

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I will try to add more comments with additional information, or submit a PR if I can!

[nicolasgarnier]

:+1: Actually I have some plan to create a standalone minisite for this repo. Just a plan now as I didn't even get started yet. (And sure, a ToC in the mean time would make sense and be nice)

With a minisite we could also list other (3rd party) repos and maybe also allow Firebase samples that are not Cloud Functions specific.

[samtstern]

I believe this is now solved in a few ways:

1. There is a TOC
2. We can customize the UX here: https://firebaseopensource.com/projects/firebase/functions-samples/