Listing RGBDS in platforms' package managers

By now RGBDS is listed on enough platforms' package managers, with various maintainers and states of updatedness. When packages are well-maintained, whether by us or third parties, it may be appropriate to mention them at https://rgbds.gbdev.io/install.

- Linux:
- `apt` (Debian, Ubuntu, Linux Mint, etc): https://packages.debian.org/testing/rgbds, https://packages.debian.org/sid/rgbds, and https://packages.ubuntu.com/resolute/rgbds
- Maintained by @avivace and @robbi-blechdose (see https://salsa.debian.org/games-team/rgbds)
- Not yet available in stable releases, but they've prepared everything so it will be
- `dnf` (Fedora, RHEL, CentOS, etc): https://packages.fedoraproject.org/pkgs/rgbds/rgbds/
- Maintained by Benjamin Lowry (blowry)
- `pacman` (Arch, Manjaro, EndeavourOS, etc): https://archlinux.org/packages/extra/x86_64/rgbds/
- Maintained by @alucryd
- `portage` (Gentoo, ChromeOS, etc): https://gpo.zugaina.org/dev-util/rgbds
- Maintained by @orbea
- [ ] *Needs updating from 1.0.1!*
- Windows:
- WinGet (first-party):
- [ ] *Not yet listed!* (see https://learn.microsoft.com/en-us/windows/package-manager/package/)
- Chocolatey (`choco`, third-party): https://community.chocolatey.org/packages/rgbds
- In progress by @Rangi42 (see https://github.com/zemzelett/chocolatey-packages)
- [ ] *Needs updating from 0.5.2!* (see #1675)
- macOS:
- Homebrew (`brew`): https://formulae.brew.sh/formula/rgbds
- Maintained automatically (see https://github.com/Homebrew/homebrew-core/pulls?q=is%3Apr+rgbds)
- MacPorts (`port`):
- [ ] *Not yet listed!* (see https://guide.macports.org/#project.contributing)
- BSD:
- `pkg` (FreeBSD): https://www.freshports.org/devel/rgbds
- Maintained by @nunotexbsd