message: document the cargo-miri feature
diff: @@ -39,7 +39,7 @@ example above), overriding it in your project directory as well, or use `rustup
  default nightly` (or `rustup default nightly-YYYY-MM-DD`) to globally make
  `nightly` the default toolchain.
  -Now you can run your project in miri:
  +Now you can run your project in Miri:
  1. Run `cargo clean` to eliminate any cached dependencies. Miri needs your
  dependencies to be compiled the right way, that would not happen if they have
  @@ -48,6 +48,19 @@ Now you can run your project in miri:
  3. If you have a binary project, you can run it through Miri using `cargo
  +nightly miri run`.
  +When running code via `cargo miri`, the `cargo-miri` feature is set. You can
  +use this to exclude test cases that will fail under Miri because they do things
  +Miri does not support:
  +
  +```rust
  +#[cfg(not(feature = "cargo-miri"))]
  +#[test]
  +fn does_not_work_on_miri() {
  + let x = 0u8;
  + assert!(&x as *const _ as usize % 4 < 4);
  +}
  +```
  +
  ### Common Problems
  When using the above instructions, you may encounter a number of confusing compiler
  