docs: add comments around how to set up env.config.js and testing with Jest

src/setupTest.jsx

@@ -67,6 +67,23 @@ jest.mock('@edx/frontend-platform/i18n', () => {
   };
 });
 
+/*
+When .env.test is removed, uncomment the env vars below and add any environment variables for testing with Jest
+
+Context: Snapshot is not currently not set up to be able to parse the environment variables in env.config.js
+*/
+
+// jest.mock('@edx/frontend-platform', () => ({
+//   getConfig: jest.fn(() => ({
+//     LMS_BASE_URL: 'http://localhost:18000',
+//     LOGOUT_URL: 'http://localhost:18000/logout',
+//     LOGO_URL: 'https://edx-cdn.org/v3/default/logo.svg',
+//     MARKETING_SITE_BASE_URL: 'http://localhost:18000',
+//     SUPPORT_URL: 'http://localhost:18000/support',
+//     OPTIMIZELY_FULL_STACK_SDK_KEY: 'SDK Key',
+//   })),
+// }));
+
 jest.mock('@edx/paragon', () => jest.requireActual('testUtils').mockNestedComponents({
   Alert: {
     Heading: 'Alert.Heading',