[ModelicaSystemOMC] add docstring for sendExpression()

Author: syntron

OMPython/ModelicaSystem.py

@@ -560,6 +560,9 @@ def buildModel(self, variableFilter: Optional[str] = None):
         self._xmlparse(xml_file=xml_file)
 
     def sendExpression(self, expr: str, parsed: bool = True) -> Any:
+        """
+        Wrapper for OMCSession.sendExpression().
+        """
         try:
             retval = self._session.sendExpression(expr=expr, parsed=parsed)
         except OMCSessionException as ex: