Add note about fixed issue in -Command parameter

Added a note as requested to describe the fixed issue with the -Command parameter of New-AzContainerGroup

Author: ssemyan

src/ContainerInstance/ContainerInstance/ChangeLog.md

@@ -22,4 +22,5 @@
 
 ## Version 1.0.0
 * General availability of `Az.ContainerInstance` module
-* Added managed identity support
+* Added managed identity support
+* Fixed issue in the -Command parameter of New-AzContainerGroup which added a trailing empty argument