Some minor issues in getting started code

Hey, while following the instructions at https://www.contentlayer.dev/docs/getting-started I ran into a number of small issues.

1. The paths config did not work for me, I'm currently just doing a direct relative import to content layer directory
2. There are various places in the code that when used lead to TS type errors.

Would a PR to address some of point (2) be welcome?