Document the status of resolver v2 support

[Shnatsel]

Cargo has made it possible to depend on the same version of a given crate with different feature sets, provided that one version is a runtime dependency and another is a build dependency.

cargo metadata somewhat notoriously is not aware of that, which leads it to conflate the build-only Cargo features with runtime features. While in reality there are two dependency graphs, cargo metadata still treats them as one. This causes the resolve graph produced by cargo metadata to include features and dependencies that aren't actually included in the build.

This is problematic for tools that need the precise dependency graph, such as cargo auditable or cargo cyclonedx.

It would be great to know whether krates overcomes this limitation, and have some example code for querying both graphs (runtime and build dependencies). It it does, then it is a big step forward for those tools!