message: update README about what we do not support
diff: @@ -38,8 +38,8 @@ cannot run all programs:
  * Miri runs the program as a platform-independent interpreter, so the program
  has no access to any platform-specific APIs or FFI. A few APIs have been
  implemented (such as printing to stdout) but most have not: for example, Miri
  - currently does not support concurrency, or networking, or file system access,
  - or gathering entropy from the system.
  + currently does not support concurrency, or SIMD, or networking, or file system
  + access.
  [rust]: https://www.rust-lang.org/
  [mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md
  