Update missing.py

Author: rustykitty

missing.py

@@ -13,6 +13,7 @@
 else:
     lang = sys.argv[1]
 
+# problem file format: NNNN-name-of-problem.lang
 pattern = re.compile(r'^(\d{4}-[a-z0-9\-]+)(\.[a-z]{2,4})$')
 
 ignored_extensions = (
@@ -41,4 +42,4 @@
 
 sol = reduce(lambda x, y: x | y, (x for x in langs.values() if x != lang))
 
-print(sol - langs[lang])
+print(sol - langs[lang])