FAQ for master password users

[sandysage]

1. inform users at download that master password is not compatible with the extension "learn more"
2. learn more links to a new FAQ entry that let's someone know to disable the addon, turn off master password, enable the addon.

[devinreams]

@sandysage here is what was added to the FAQ:

https://lockwise.firefox.com/faq.html#does-firefox-lockwise-for-desktop-addon-work-with-the-master-password-feature-in-firefox

This does not inform the user "at download". Would you like us to brainstorm some approaches on how to present this up-front a bit more?