Add link to C API docs

Author: crandmck

sidebars.js

@@ -245,6 +245,11 @@ const sidebars = {
           id: 'c2pa-c/docs/supported-formats',
           label: 'Supported media formats',
         },
+        {
+          type: 'link',
+          label: 'API documentation',
+          href: 'https://contentauth.github.io/c2pa-c/annotated.html',
+        },
         {
           type: 'link',
           label: 'GitHub',