Make imports/exports not be a dropdown in sidebar (#19907)

* Don't make a section be a dropdown if it has no child links

* - Cleaned up code

- Updated tests

* Document what the 'if' is checking

config/nimdoc.cfg

@@ -16,6 +16,14 @@ doc.section = """
 </div>
 """
 
+# Just a single item in the TOC (e.g. imports, exports)
+doc.section.toc_item = """
+<li>
+  <a class="reference reference-toplevel" href="#$sectionID" id="$sectionTitleID">$sectionTitle</a>
+</li>
+"""
+
+# This is a section (e.g. procs, types) in the TOC which gets turned into a drop down
 doc.section.toc = """
 <li>
   <details open>