Bintray Deprecation

[SmiVan]

As mentioned in #10, Bintray is being shut down on 2021-05-01, and recently the repo stopped being signed.

E: Failed to fetch https://dl.bintray.com/dryzig/zig-ubuntu/dists/focal/InRelease  403  Forbidden [IP: 3.125.168.216 443]
E: The repository 'https://dl.bintray.com/dryzig/zig-ubuntu focal InRelease' is no longer signed.

[SmiVan]

I've taken the link to this repo out of the Zig installation instructions for now, so newcomers will not be mislead.

If and when a new repo will become available, this should be re-linked in the installation instructions.

[TedHartDavis]

This is annoying, now that it's simply providing a 502.

[nfultz]

Should probably remove / comment out the links from this repos' README also, I was disappointed it didn't work

[rdebath]

Um, so where's this? Perhaps a github.io page off the gh-pages branch?

[sskras]

Yeah, what's the deal? Ping @artob :)