[hotfix][docs] Fix ToC to include H1

This closes apache#3773.

Author: rmoff

docs/config.toml

@@ -65,6 +65,8 @@ pygmentsUseClasses = true
 [markup]
 [markup.goldmark.renderer]
   unsafe = true
+[markup.tableOfContents]
+  startLevel = 1
 
 [languages]
 [languages.en]
@@ -91,4 +93,4 @@ source = 'layouts'
 target = 'layouts'
 [[module.imports.mounts]]
 source = 'data'
-target = 'data'
+target = 'data'