Check isPrimaryKey: add comment abound columns Scala type conversion.

Author: nikie

pydeequ/checks.py

@@ -250,6 +250,7 @@ def isPrimaryKey(self, column, *columns, hint=None):
         :param str hint: A hint that states why a constraint could have failed.
         :return: isPrimaryKey self: A Check.scala object that asserts completion in the columns.
         """
+        # This relies on Py4J's implicit conversion from Seq to varargs:
         columns_seq = to_scala_seq(self._jvm, columns)
         hint = self._jvm.scala.Option.apply(hint)
         self._Check = self._Check.isPrimaryKey(column, hint, columns_seq)