Update the how to tag files to include the fact that picard is not a mass tagger

We should let people know that picard is not built to be a mass-single-track/recording tagger/tag fixer.

Picard believes in quality over quantity and provides a plethora of customizations to tweak tags to your needs.

https://community.metabrainz.org/t/picard-survey-and-first-impressions/189889