stack opcode example comments (#3546)

* stack opcode example comments

* move index into example

---------

Co-authored-by: Jimmy <jinghui@wayne.edu>

src/Neo.VM/OpCode.cs

@@ -725,6 +725,10 @@ public enum OpCode : byte
         /// <summary>
         /// The item n back in the stack is copied to the top.
         ///
+        /// <example> a b c d 2 -> a b c d b
+        ///  index => 3[2]1 0
+        /// </example>
+        /// 
         /// <remarks>
         ///     Push: 1 item(s)
         ///     Pop: 0 item(s)
@@ -735,6 +739,8 @@ public enum OpCode : byte
         /// <summary>
         /// The item at the top of the stack is copied and inserted before the second-to-top item.
         ///
+        /// <example> a b c -> a c b c </example>
+        /// 
         /// <remarks>
         ///     Push: 1 item(s)
         ///     Pop: 0 item(s)
@@ -769,6 +775,10 @@ public enum OpCode : byte
         /// <summary>
         /// The item n back in the stack is moved to the top.
         ///
+        /// <example>a b c d 2 -> a c d b
+        /// index => 3[2]1 0
+        /// </example>
+        /// 
         /// <remarks>
         ///     Push: 0 item(s)
         ///     Pop: 1 item(s)
@@ -793,7 +803,6 @@ public enum OpCode : byte
         ///
         /// <example> a b c d -> d c b a</example>
         ///
-        ///
         /// <remarks>
         ///     Push: 0 item(s)
         ///     Pop: 0 item(s)
@@ -804,7 +813,8 @@ public enum OpCode : byte
         /// <summary>
         /// Pop the number N on the stack, and reverse the order of the top N items on the stack.
         ///
-        ///
+        /// <example> a b c d 3 -> a d c b </example>
+        /// 
         /// <remarks>
         ///     Push: 0 item(s)
         ///     Pop: 1 item(s)