docs: add comment explaining how to reactivate code signing

packages/desktop-electron/afterSignHook.js

@@ -2,6 +2,12 @@ const fs = require('fs');
 const path = require('path');
 var electron_notarize = require('electron-notarize');
 
+// This is expected to be run by `electron-builder` after it signs the build.
+// It's disabled for now as we currently don't sign builds after Actual being open sourced.
+// To start signing builds again:
+// - add the property `"afterSign": "./afterSignHook.js"` to the `build` object in package.json.
+// - add the property `"certificateSubjectName": "Shift Reset LLC"` (or similar) to the `win` object in package.json.
+
 module.exports = async function(params) {
   // Only notarize the app on Mac OS only.
   if (process.platform !== 'darwin' || process.env['SKIP_NOTARIZATION']) {