pages: add sigil generator

[matildepark]

In which we speedrun writing our own https://sigil-generator.vercel.app.

@gordoncc What should we be doing with the copy on this page?

[thelifeandtimes]

I'd suggest echoing some of the copy/messaging on this page: https://urbit.org/overview/urbit-id

edit: along with explanation that this is a sigil generator....

[gordoncc]

Neat!

1. This is clearly not the Urbit ID page, but its own Sigil Generator page.
2. This should be linked to from an Urbit ID page, which does not yet exist. Someone should probably write and design that, I guess that someone is probably me.
3. /ids should probably redirect to an IDs section in the ecosystem. Except it seems odd to call it "IDs" – I guess we could call it "Ships" but that might even be more confusing.

[matildepark]

I think it is cool anyway and I felt like doing it for fun.