Add exception for RawSecurityDescriptor constructor (#4050)

Author: nxtn

xml/System.Security.AccessControl/RawSecurityDescriptor.xml

@@ -72,6 +72,7 @@
         <param name="sddlForm">The SDDL string from which to create the new <see cref="T:System.Security.AccessControl.RawSecurityDescriptor" /> object.</param>
         <summary>Initializes a new instance of the <see cref="T:System.Security.AccessControl.RawSecurityDescriptor" /> class from the specified Security Descriptor Definition Language (SDDL) string.</summary>
         <remarks>To be added.</remarks>
+        <exception cref="T:System.ArgumentException">The SDDL form of a security descriptor object is invalid.</exception>
       </Docs>
     </Member>
     <Member MemberName=".ctor">