Make sure to actually use yarn to install the main-packages, otherwise the packages.json#resolutions property will not be used and @babel/helpers would not get overruled

Overruled @babel/helpers to fix how initializers play with decorated properties. Thus circumventing the imperformant and lengthy code being generated by babel in the non-legacy option.

packages/babel-helpers/README.md

@@ -0,0 +1,19 @@
+# @babel/helpers
+
+> Collection of helper functions used by Babel transforms.
+
+See our website [@babel/helpers](https://babeljs.io/docs/en/next/babel-helpers.html) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/helpers
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/helpers --dev
+```