Document System.Security.AccessControl.ObjectSecurity.SecurityDescriptor (#2900)

* Document System.Security.AccessControl.ObjectSecurity.SecurityDescriptor

* suggestion by rpetrusha

Co-Authored-By: Ron Petrusha <[email protected]>

Author: carlossanlop

xml/System.Security.AccessControl/ObjectSecurity.xml

@@ -1267,8 +1267,8 @@
         <ReturnType>System.Security.AccessControl.CommonSecurityDescriptor</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets the security descriptor for this instance.</summary>
+        <value>The security descriptor for this instance.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1695,4 +1695,4 @@
       </Docs>
     </Member>
   </Members>
-</Type>
+</Type>