rustc_pull: explain order of operations

Author: RalfJung

src/tools/miri/miri-script/src/commands.rs

@@ -239,6 +239,8 @@ impl Command {
         // the merge has confused the heck out of josh in the past.
         // We pass `--no-verify` to avoid running git hooks like `./miri fmt` that could in turn
         // trigger auto-actions.
+        // We do this before the merge so that if there are merge conflicts, we have
+        // the right rust-version file while resolving them.
         sh.write_file("rust-version", format!("{commit}\n"))?;
         const PREPARING_COMMIT_MESSAGE: &str = "Preparing for merge from rustc";
         cmd!(sh, "git commit rust-version --no-verify -m {PREPARING_COMMIT_MESSAGE}")