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.

PR-URL: #30772
Reviewed-By: Beth Griggs <[email protected]>
Reviewed-By: David Carlier <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Rich Trott <[email protected]>