Update baseURL to use dynamic VERCEL_BRANCH_URL

Signed-off-by: Aviv Keller <me@aviv.sh>

Author: avivkeller

doc-kit.config.mjs

@@ -11,7 +11,7 @@ export default {
     // Important Configuration
     project: 'Node.js',
     title: '{project} Learn',
-    baseURL: 'https://nodejs.org/learn',
+    baseURL: `https://${process.env.VERCEL_BRANCH_URL ?? 'nodejs.org'}/learn`,
     pageURL: '{baseURL}{path}.html',
     editURL: 'https://github.com/nodejs/learn/edit/main/pages{path}.md',
     useAbsoluteURLs: true,