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It seems in it's infancy.

The front page says it's supported by retroarch, but you go to their docs section, there's nothing there.

Looking forward to a straightforward way to put acheivements into my retroarch, and not piecemeal by emulator.

It's been around for a while. It's more of a lack of docs than lack of support. RA has docs directly: https://www.retroarch.com/?page=achievements

Support for RetroAchievements is builtin to RetroArch [1]. You should just need to enter your credentials.