tracing-subscriber: link init docs in description of tracing-log feature flag

[jaskij]

Motivation

When updating my project after a time of inactivity, I reviewed feature flags of tracing_subscriber, and decided to enable the tracing-log feature. This, inevitably lead to a panic in my wrapper, which has function like so:

pub fn init_short_logs(filter: impl Into<EnvFilter>) {
    tracing_subscriber::fmt()
        .with_env_filter(filter)
        .with_span_events(FmtSpan::CLOSE)
        .with_writer(std::io::stdout)
        .compact()
        .init();
}

Solution

To reduce future confusion, this PR adds a link to tracing_subscriber::util::SubscriberInitExt in the description of the feature flag.