ring is affected by a nightly Cargo regression

[oconnor663]

Ring seems to have the same issue as e.g. the remove_dir_all crate had, with the most recently nightly toolchain:

error: failed to download `ring v0.16.14`

Caused by:
  unable to get packages from source

Caused by:
  failed to parse manifest at `/home/jacko/.cargo/registry/src/github.com-1ecc6299db9ec823/ring-0.16.14/Cargo.toml`

Caused by:
  readme file with name 'doc/link-to-readme.md' was not found

This is tracked at rust-lang/cargo#8351 and already fixed by rust-lang/cargo#8353. However, to unbreak callers until the next nightly goes out, it might be nice to fix the error downstream.

[briansmith]

Thanks. I think PR #1010 will fix this.