Main README dead link

[lianakoleva]

"GNU toolchain port for v0.8" points to https://github.com/riscv-collab/riscv-gnu-toolchain/tree/rvv-0.8.x, which is no longer a branch of the repo.

[aswaterman]

If you don't mind making a PR that fixes the broken link, we'll happily merge it.

[lianakoleva]

I'm not sure what it should be replaced with. All RVV branches have been deleted from that repo. See riscv-gnu-toolchain/issue1308 for the discussion. Maybe issue1301 or PR109 can provide some insight.

[aswaterman]

I don't know how to address this issue if we don't know how to update the README. Feel free to submit a PR that deletes the offending link. Closing in the interim.