According to [the npm config
docs](https://docs.npmjs.com/misc/config#npmrc-files), a user can
specify the path to their `npmrc` files using the environment
variables `NPM_CONFIG_USERCONFIG` and `NPM_CONFIG_GLOBALCONFIG`. When
set, these variables should override the default paths.
This adds extensive option checking and error handling with the goal to catch user errors as early in the process as possible. Bad option combinations and/or values will result in actionable information and stop the process before network access and processing occurs.
If no version specifier is supplied `ng add` will now try to find the most recent version of the package that has peer dependencies that match the package versions supplied in the project's package.json
