Add a comment in .github/workflows/ci.yml

Author: hyd-dev

.github/workflows/ci.yml

@@ -74,6 +74,7 @@ jobs:
           else
             RUSTC_HASH=$(< rust-version)
           fi
+          # We need a nightly cargo for parts of the cargo miri test suite.
           rustup-toolchain-install-master \
             -f \
             -n master "$RUSTC_HASH" \