message: Document MIRI_AUTO_OPS
diff: @@ -393,6 +393,9 @@ Some native rustc `-Z` flags are also very relevant for Miri:
  Moreover, Miri recognizes some environment variables:
  +* `MIRI_AUTO_OPS` indicates whether the automatic execution of rustfmt, clippy and rustup-toolchain
  + should be skipped. If it is set to any value, they are skipped. This is used for avoiding
  + infinite recursion in `./miri` and to allow automated IDE actions to avoid the auto ops.
  * `MIRI_LOG`, `MIRI_BACKTRACE` control logging and backtrace printing during
  Miri executions, also [see "Testing the Miri driver" in `CONTRIBUTING.md`][testing-miri].
  * `MIRIFLAGS` (recognized by `cargo miri` and the test suite) defines extra
  