chore(linux): Update readme

This change adds separate READMEs for the legacy projects, and
removes mentioning of the legacy projects in the current READMEs.
The motivation is to make it later easier to remove the legacy
projects, as well as reducing the efforts to testing the README with
legacy projects. Since legacy projects aren't maintained anymore
it doesn't make sense to still have them in the regular README,
suggesting that the instructions work for the legacy projects as
well.