Add comment about "interesting" HTTP handling by HedgeDoc

import_md/hedgedoc_import.py

@@ -16,6 +16,7 @@ def import_single_document(instance_url, hedgedoc_free_url, content, session_id)
     headers = {"Cookie": f"connect.hedgeDoc.sid={session_id}", "Content-Type": "text/markdown"}
 
     req = urllib.request.Request(request_url, data=str.encode(content), method='POST', headers=headers)
+    # unfortunately, no error is thrown if a document is not created when session cookie is invalid
     with urllib.request.urlopen(req) as response:
         return response.url