message: expand flag docs
diff: @@ -240,9 +240,12 @@ environment variable:
  future use of it will error). This helps you in finding out why UB is
  happening and where in your code would be a good place to look for it.
  * `-Zmiri-track-raw-pointers` makes Stacked Borrows track a pointer tag even for
  - raw pointers. This can make valid code fail to pass the checks (when
  - integer-pointer casts are involved), but also can help identify latent
  - aliasing issues in code that Miri accepts by default.
  + raw pointers. This can make valid code fail to pass the checks, but also can
  + help identify latent aliasing issues in code that Miri accepts by default. You
  + can recognize false positives by "<untagged>" occurring in the message -- this
  + indicates a pointer that was cast from an integer, so Miri was unable to track
  + this pointer. Make sure to use a non-Windows target with this flag, as the
  + Windows runtime makes use of integer-pointer casts.
  Some native rustc `-Z` flags are also very relevant for Miri:
  