That's basically what cheat.sh does. It's an editable wiki that contains common use cases (cheat sheets) and can be called directly from the command-line, e.g.:

    curl cheat.sh/ffmpeg
    curl cheat.sh/youtube-dl
    curl cheat.sh/cd
    curl cheat.sh/find

It gives quite a bit more than 3 use cases, but you could do:

    curl -s cheat.sh/ffmpeg | head

For more details you can go to the site in a browser or use:

    curl cheat.sh
    curl cheat.sh/:help