feat: add configurations for TOC component

src/config.ts

@@ -24,6 +24,10 @@ export const siteConfig: SiteConfig = {
       url: ''                // (Optional) URL link to the original artwork or artist's page
     }
   },
+  toc: {
+    enable: true,           // Display the table of contents on the right side of the post
+    depth: 2                // Maximum heading depth to show in the table, from 1 to 3
+  },
   favicon: [    // Leave this array empty to use the default favicon
     // {
     //   src: '/favicon/icon.png',    // Path of the favicon, relative to the /public directory