Lastly, there is a hint in the Tone.js source code and what function to call with your button press / touch:
///////////////////////////////////////////////////////////////////////////
// CONTEXT
///////////////////////////////////////////////////////////////////////////
/**
* The shared AudioContext
* @type {Tone.Context}
* @private
*/
Tone._audioContext = null;
/**
* Most browsers will not play _any_ audio until a user
* clicks something (like a play button). Invoke this method
* on a click or keypress event handler to start the audio context.
* More about the Autoplay policy [here](https://developers.google.com/web/updates/2017/09/autoplay-policy-changes#webaudio)
* @memberOf Tone
* @static
* @return {Promise} This promise is resolved when the audio context is started.
* @example
* document.querySelector('#playbutton').addEventListener('click', () => Tone.start())
*/
Tone.start = function(){
return Tone.context.resume();
};