chore: Add code comments.

src/main.js

@@ -249,6 +249,7 @@ function dispatch(event) {
    * https://github.com/jaywcjlove/hotkeys/pull/129
    * This solves the issue in Firefox on Windows where hotkeys corresponding to special characters would not trigger.
    * An example of this is ctrl+alt+m on a Swedish keyboard which is used to type μ.
+   * Browser support: https://caniuse.com/#feat=keyboardevent-getmodifierstate
    */
   if (event.getModifierState && event.getModifierState('AltGraph')) {
     _downKeys.push(17, 18);