Revert "Remove Acorn as dependency; treat as requirement (#2825)" (#2826)

This reverts commit 653832edb2.

bootstrap/app.php

@@ -11,13 +11,7 @@
 |
 */
 
-try {
 \Roots\bootloader();
-} catch (Throwable $e) {
-    wp_die(
-        __('You need to install Acorn to use this theme.', 'sage')
-    );
-}
 
 /*
 |--------------------------------------------------------------------------

composer.json

@@ -39,7 +39,8 @@
     }
   },
   "require": {
-    "php": "^7.3|^8.0"
+    "php": "^7.3|^8.0",
+    "roots/acorn": "2.0.0-alpha.0"
   },
   "require-dev": {
     "filp/whoops": "^2.12",