FAQ (wiki): update to reflect integration of MP3 exporting

I see that LAME is now integrated in Audacity.

Great news and great job!

Perhaps the FAQ should be updated to reflect this.

The FAQ was updated when we integrated LAME: https://manual.audacityteam.org/man/faq_installation_and_plug_ins.html#lame

And the front page in the Manual s an entry that reads:

LAME MP3 export and FFmpeg import/export libraries for more formats

Clicking on the LAME link there takes you to the above FAQ