Add documentation re: permissions for Electron

[beaugunderson]

I could not initialize WebMidi in my Electron renderer process until I figured out that I needed to handle the permissions requests and checks, like so, in the main process:

  mainWindow.webContents.session.setPermissionRequestHandler((webContents, permission, callback, details) => {
    if (permission === 'midi' || permission === 'midiSysex') {
      callback(true);
    } else {
      callback(false);
    }
  })

  mainWindow.webContents.session.setPermissionCheckHandler((webContents, permission, requestingOrigin) => {
    if (permission === 'midi' || permission === 'midiSysex') {
      return true;
    }

    return false;
  });

Documenting this will save the next person some time. :)

[djipco]

That's a good idea. Would you be willing to update the default Electron example to include it? I added an Electron page to the documentation.

[beaugunderson]

Here you go! https://github.com/djipco/webmidi/pull/381

[djipco]

Awesome, thanks!