Swiftly PGP signature link points to wrong URL

[jakepetroules]

Describe the bug

The PGP signature link under the Swiftly for Linux download points to the wrong URL. It's pointed at the signature for the x86_64 0.4.0 release, but the current is 1.0.1. Also, the links don't account for multiple architectures.

To Reproduce

Steps to reproduce the behavior:

1. Go to https://www.swift.org/install/linux/
2. Click on 'PGP: Signature' under Swiftly

Expected behavior

I would expect this to be laid out more similarly to the Swift toolchain itself, with 4 distinct links, like:

Download (x86_64) | Signature (PGP)
Download (aarch64) | Signature (PGP)

Actual behavior

There's only a link to the PGP signature for the obsolete 0.4.0 release and only for the x86_64 architecture.