chore: add section to socialize

[ovflowd]

This PR adds a "socialize" with Node.js Dev section redirecting to our official community (aka the Discord server)

[Trott]

I think changes to these kinds of documents that will show up in all our repos probably warrants a TSC ping: @nodejs/tsc

[Trott]

Is the Discord server out of place here? It's already the very first item in the get-involved document linked previously in the list.

[ovflowd]

Is the Discord server out of place here? It's already the very first item in the get-involved document linked previously in the list.

In which list? 👀 — anyhow completely fine not merging this. It was a stretch but I felt at least one social option could be listed within our README

[Trott]

In which list?

In this PR, the Discord server is being added as a fifth item in a list of links. (It doesn't use an HTML list element, but if we were using semantic markup, it would.) That's the list I'm talking about. And the third item in that list is a link to https://nodejs.org/en/get-involved, where the Discord server is the first thing linked in the body of that document.