How to commit if changes done

--quiet flag disables default output of diff and implies --exit-code.

--exit-code flag makes the command exit with 1 if there were differences and 0 otherwise no differences.

git diff --quiet || (git add README.md && git commit -m "Updated README")

This works because in case of an OR operator, evaluation of RHS is dependent on the result of RHS. If LHS returns 1, no RHS evaluation.