make sure we don't install more than we have to

Author: RalfJung

README.md

@@ -105,6 +105,7 @@ nightly that *does* come with Miri:
 ```sh
 MIRI_NIGHTLY=nightly-$(curl -s https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/miri)
 echo "Installing latest nightly with Miri: $MIRI_NIGHTLY"
+rustup set profile minimal
 rustup default "$MIRI_NIGHTLY"
 
 rustup component add miri