Auto merge of #1759 - RalfJung:readme, r=RalfJung

mention 'cargo miri test filter' in README

Also update the "unsupported" example to something that is actually unsupported.

README.md

@@ -92,8 +92,11 @@ Now you can run your project in Miri:
 The first time you run Miri, it will perform some extra setup and install some
 dependencies. It will ask you for confirmation before installing anything.
 
-`cargo miri run/test` supports the exact same flags as `cargo run/test`.  You
-can pass arguments to Miri via `MIRIFLAGS`. For example,
+`cargo miri run/test` supports the exact same flags as `cargo run/test`. For
+example, `cargo miri test filter` only runs the tests containing `filter` in
+their name.
+
+You can pass arguments to Miri via `MIRIFLAGS`. For example,
 `MIRIFLAGS="-Zmiri-disable-stacked-borrows" cargo miri run` runs the program
 without checking the aliasing of references.
 
@@ -105,9 +108,7 @@ Miri does not support:
 #[test]
 #[cfg_attr(miri, ignore)]
 fn does_not_work_on_miri() {
-    std::thread::spawn(|| println!("Hello Thread!"))
-        .join()
-        .unwrap();
+    tokio::run(futures::future::ok::<_, ()>(()));
 }
 ```