message: Document unstable --build-plan
diff: @@ -254,3 +254,16 @@ for each optional dependency, implicit features get created for any optional
  dependencies where a feature of the same name is not defined. However, if
  a feature of the same name as a dependency is defined, that feature must
  include the dependency as a requirement, as `foo = ["crate:foo"]`.
  +
  +
  +### Build-plan
  +* Tracking Issue: [rust-lang/cargo#5579](https://github.com/rust-lang/cargo/issues/5579)
  +
  +The `--build-plan` argument for the `build` command will output JSON with
  +information about which commands would be run without actually executing
  +anything. This can be useful when integrating with another build tool.
  +Example:
  +
  +```
  +cargo +nightly build --build-plan -Z unstable-options
  +```
  