doc: mention N-API as recommended approach

We've had a few comments that from the doc it might not
be clear that N-API is the recommended approach for Addons.
As a start, mention N-API early in the non N-API section
as the recommended approach unless lower level access
is required.

PR-URL: https://github.com/nodejs/node/pull/28922


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>