message: Prevent mistakes with beta branch on cargo
diff: @@ -63,12 +63,13 @@ minor version of master. First determine the branch point for cargo in
  `rust-lang/rust`, and then create a new branch:
  ```sh
  -$ cd rust
  -$ git fetch rust-lang
  -$ CARGO_SHA=`git rev-parse $BRANCH_POINT:src/tools/cargo`
  -$ cd src/tools/cargo
  -$ git branch rust-1.YY.0 $CARGO_SHA
  -$ git push origin rust-1.YY.0
  +cd rust
  +git fetch rust-lang
  +NEW_BETA_VERSION=`git show $BRANCH_POINT:src/version`
  +CARGO_SHA=`git rev-parse $BRANCH_POINT:src/tools/cargo`
  +cd src/tools/cargo
  +git branch rust-$NEW_BETA_VERSION $CARGO_SHA
  +git push origin rust-$NEW_BETA_VERSION
  ```
  You'll need to temporarily disable branch protection on GitHub to push the new
  