Add member count to the `README.md` document

[shtlrs]

Currently, we only state that we're a large community, but the real scale isn't properly inferred there.

I'd like to back that up with a number (because it's cooler), and that number being how many members we have.

This is possible by making an endpoint in our site project that'll query the number of members we have based on our server's invite link.
Including the with_counts query parameter will do that as defined here.

Then in the markdown, we'll just have a hyperlink that'll use that endpoint.

If there are other suggestions to do this, i'd be interested to find out more

[shenanigansd]

You can do this without an extra endpoint. Take a look at https://github.com/Ukraine-Relief-Efforts
In the README I have:
[![Discord](https://img.shields.io/discord/946624673200893953.svg?label=TechFor&logo=discord)](https://discord.gg/4bQvrgXbxW)
Which renders as

[shtlrs]

That only fetches the online count though, not the total number of members, does it ?