doc: briefly explain what's included
doc: briefly explain what's included

PR-URL: https://github.com/npm/npm/pull/11188
Credit: da39a3ee5e6b4b0d3255bfef95601890afd80709@beaugunderson
Reviewed-By: da39a3ee5e6b4b0d3255bfef95601890afd80709@othiym23

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