Add developer doc to explain how contributors and developers on the team should
treat the `package.json` file now that `angular-cli` in a mixed mode of
yarn workspaces and Bazel.
This should make it easier to manage and diff. This takes 2 things into account:
1. we have either stable or experimental versions and each are kept in monorepo.
2. we dont keep hash and update only changed packages.
This commit also removed the hash to make sure this does not happen.
