Added information (#26367)

Added information to foreach loop. Indicated foreach loop is read only.

guide/english/csharp/foreach/index.md

@@ -6,6 +6,8 @@ title: Foreach Loop
 
 The `foreach` loop executes a block of code for each item in a collection. The benefit of the `foreach` loop is you need not know how many items are within the collection to iterate through it; you simply tell your `foreach` loop to loop through the collection, as long as there are items within it. It is useful for iterating through lists, arrays, datatables, IEnumerables and other list-like data structures. It can be less efficient than a very well designed `for` loop, but the difference is negligible in most cases.
 
+It is worth noting however, that when a `foreach` loop iterates through a data structure, each variable is read-only. Ideally, when you want to modify data in a loop, a `for` loop is the better choice. 
+
 ### Example
 ```csharp