message: update unsupported example in README (now that threading is supported on some platforms)
diff: @@ -112,7 +112,7 @@ There is no way to list all the infinite things Miri cannot do, but the
  interpreter will explicitly tell you when it finds something unsupported:
  ```
  -error: unsupported operation: Miri does not support threading
  +error: unsupported operation: can't call foreign function: bind
  ...
  = help: this is likely not a bug in the program; it indicates that the program \
  performed an operation that the interpreter does not support
  