Added notice that facial detection is occurring

[mrkmg]

Added a pam conversation message that the facial detection is being performed.

Why?

In my setup, my webcam is not always "front and center". I often use external monitors on my laptop and my webcam ends up pointing toward the side of my face. In order to get face detection to work, I need to turn my head and look into the webcam.

I find myself forgetting to turn and look at the webcam when typing sudo from the command line. Then I either type my password or canceling it and trying again.

I added this message on my machine, and it works great to remind me to look at the webcam.

[boltgolt]

Thanks for adding your work back into Howdy!
Because this is new behavior that all users will see after the update to 2.5.0, i would rather have that it could be turned on or off with a config value. Would you be comfortable with adding a value to the [core] section of the config file?

[mrkmg]

I assume we want this to be config off by default?

[boltgolt]

Thanks a lot!