Auto merge of #1030 - RalfJung:mir-opt-comment, r=RalfJung
Auto merge of #1030 - RalfJung:mir-opt-comment, r=RalfJung

update comment re: not using higher mir-opt-level

rust-lang/miri,rust-lang/miri,tsion/miri,rust-lang/miri,rust-lang/miri