Add info about distro/community repos for Swift Linux package

[parpok]

Is your feature request related to a problem? Please describe

Getting started on platforms that aren't Mac can be a bit problematic. There are easier solutions however they aren't listed on the downloads page so listing those simple solutions would make Swift more accessible to everyone outside of the Mac ecosystem.

Describe the solution you'd like

Add information about Linux Distro package managers and repositories such as Fedora RPM repo for swift, Arch Linux implementation variants or even community Ubuntu/Debian repo for users who don't want to install it manually for example

Describe alternatives you've considered

Maybe forking and adding that info manually and submitting a pull request that could solve this small issue.

Additional context

For some people getting Swift ready on their machine that isn't a Mac could be complicated. On Linux only available information is for mainly enterprise/specialty distros (like CentOS or Amazon Linux) that most people don't use or how to manually install everything - which can take some time and requires a little more Linux skills. Adding easy to use options for more common user distros like Fedora or Ubuntu could help with some people getting into Swift.

Also since Windows version is maintained by community members why not also let users install swift using a community package on Linux too from AUR or somewhere else.