feat: add end-of-support warning (#14714)

The 1.7 series has reached the end of its support window.

lib/browser/api/app.js

@@ -61,6 +61,14 @@ if (process.platform === 'linux') {
   }
 }
 
+// end-of-life support warning. goodbye, `electron/1-6-x` ...
+console.warn(
+  'Electron 1.7.x has reached the end of its support cycle.\n',
+  'Developers are encouraged to upgrade their applications to a newer series.\n',
+  'Read about newer series at https://electronjs.org/releases .\n',
+  'Read about Electron support at https://electronjs.org/docs/tutorial/support#supported-versions .'
+)
+
 app.allowNTLMCredentialsForAllDomains = function (allow) {
   if (!process.noDeprecations) {
     deprecate.warn('app.allowNTLMCredentialsForAllDomains', 'session.allowNTLMCredentialsForDomains')