enter xml file name to use through command line

tools/variableHouseoldToWikiTable.py

 #!/usr/bin/python3
 
+import sys
 import xml.etree.ElementTree as ET
 
 
@@ -50,6 +51,13 @@ def parseDirectory(directory, cwd, stripDescriptionPrefix) :
     parseDirectory(elem, cwd+"/"+elem.attrib["name"], len(dirdescription)+1)
       
 
+if len(sys.argv) != 2 :
+  print("Usage: variableHouseholdToWikiTable.py <xml_file_name>")
+  sys.exit(1)
+
+filename=sys.argv[1]
+
+
 print("^ PV name           ^ Type          ^ Unit    ^ Description   ^")
     
 tree = ET.parse("llrfctrl.xml")