Show the standalone installers for earlier releases (`FIXME`)

[ojeda]

While it is currently easy to figure out the URLs for older releases, it would be better to have a way to show the earlier releases somehow.

There is a FIXME comment about it in the docs:

rust-forge/src/infra/other-installation-methods.md

Lines 99 to 101 in 7932498

	<!-- FIXME: Show this sentence again once we've found a quick way to display the archives.
	Past releases can be found in [the archives].
	-->

[yerke]

@ojeda Are you looking for a way to list installers just for stable channel or all channels? If we decide to show nightly, the list will be too long.

[ojeda]

For our use case, only stable releases (and I would imagine it is also the most important case for others too).

Thanks!

[yerke]

My WIP PR is here: #733