docs: add v1.x/v2.0-rc.x notices

Author: nklayman

docs/.vuepress/config.js

@@ -19,6 +19,11 @@ module.exports = {
     nav: [
       { text: 'Home', link: '/' },
       { text: 'Guide', link: '/guide/' },
+      {
+        text: 'v1.x',
+        link:
+          'https://github.com/nklayman/vue-cli-plugin-electron-builder/tree/v1'
+      },
       {
         text: 'Changelog',
         link:

docs/guide/README.md

@@ -3,6 +3,10 @@ title: Quick Start
 sidebarDepth: 2
 ---
 
+:::warning
+These are the docs for the v2.0-rc release line, which is recommended over the v1.x version. The old docs are available [here](https://github.com/nklayman/vue-cli-plugin-electron-builder/tree/v1/docs). To upgrade, see the [release announcement](https://github.com/nklayman/vue-cli-plugin-electron-builder/releases/tag/v2.0.0-rc.1).
+:::
+
 # Quick Start
 
 ::: warning Important