Document manifest options
All built-in cargo commands have this output included when run with `cargo foo --help`. Clippy is the only exception, so I have copied the text here. As far as I can tell, the flags come from Cargo itself and not clippy, but the user almost certainly does not care about that.
```text
Manifest Options:
--manifest-path <PATH> Path to Cargo.toml
--frozen Require Cargo.lock and cache are up to date
--locked Require Cargo.lock is up to date
--offline Run without accessing the network
```
changelog: Add the standard Manifest Options section to the `--help` output
346b094a11