docs: fix sub-packages docs default public_api location (#928)
docs: fix sub-packages docs default public_api location (#928)

The default location for `public_api.ts` in a sub-package is within the `package-name/src` dir not in the root of the sub-package.
dherges/ng-packagr,dherges/ng-packagr,dherges/ng-packagr,dherges/ng-packagr