Include cargo tree -i <crate> output in issue

[Nemo157]

Motivation

First step of triaging an audit issue is to see why the affected crate is being included in the build, to see if it's a direct dependency that can be controlled, or a deep dependency that may need more effort. Including the output from cargo tree -i <crate> in the opened issue would allow trivially seeing this from the issue directly (example).

[svartalf]

Hi, @Nemo157! I agree that adding it would be very helpful; I'm aiming to get this information from cargo-audit directly, see rustsec/rustsec#227 (comment)