Rust packaging guidelines: Remove --all-features suggestion

hello, following up on an irc discussion on the Rust packaging guideline, I'd like to propose changing the command in section 5 from: cargo build --frozen --release --all-features to cargo build --frozen --release Enabling all non-default features is rarely what we want, they are usually off for a reason and instead features should be explicitly selected and enabled, or added to the default feature set by upstream if they are meant to be on by default. Setting --all-features in many projects (mine included) would enable the `vendored` feature that opts you out of system libraries, which is something we explicitly don't want. cheers, kpcyrd