message: doc: clarify bytes::Regex docs for 's' flag
  The old docs weren't as clear as they could be with
  respect to how the `s` and `u` flags interacted.
  PR
diff: @@ -731,8 +731,8 @@ Unicode codepoints. For example, in ASCII compatible mode, `\xFF` matches the
  literal byte `\xFF`, while in Unicode mode, `\xFF` is a Unicode codepoint that
  matches its UTF-8 encoding of `\xC3\xBF`. Similarly for octal notation when
  enabled.
  -6. `.` matches any *byte* except for `\n` instead of any Unicode scalar value.
  -When the `s` flag is enabled, `.` matches any byte.
  +6. In ASCII compatible mode, `.` matches any *byte* except for `\n`. When the
  +`s` flag is additionally enabled, `.` matches any byte.
  # Performance
  