doc: improve napi formatting

This addresses two nits:

1. Bullet points that span over multiple lines should be indented consitently. Otherwise they are not always properly highlighted.
2. Lines breaks after titles improve the readability.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines