GPG signing documentation is broken

[ffaf1]

ghcup-metadata/README.md

Lines 121 to 128 in fc022fd

	#### GPG signing
	- make sure to sign the yaml files you edited, e.g.: `gpg --detach-sign -u <your-email> ghcup-0.0.8.yaml` or ask a GHCup developer to sign
	- PGP pubkeys need to be cross-signed by the GHCup team
	- they need to be added to the CI: https://github.com/haskell/ghcup-metadata/blob/develop/.github/workflows/sigs
	- and need to be documented on the homepage
	* https://github.com/haskell/ghcup-hs/blob/master/docs/guide.md#gpg-verification
	* https://github.com/haskell/ghcup-hs/blob/master/docs/install.md#unix

Last two links are 404.