Update parser.py documentation with a warning/clarification.

Author: nitram2342

libnmap/parser.py

@@ -34,7 +34,9 @@ def parse(cls, nmap_data=None, data_type="XML", incomplete=False):
 
         :param incomplete: enable you to parse interrupted nmap scans \
         and/or incomplete nmap xml blocks by adding a </nmaprun> at \
-        the end of the scan.
+        the end of the scan. Be aware that this flag does not work for \
+        already valid XML files, because adding an XML tag will \
+        invalidate the XML.
         :type incomplete: boolean
 
         As of today, only XML parsing is supported.