Add code example for CA1002 rule (#48762)

docs/fundamentals/code-analysis/quality-rules/ca1002.md

@@ -10,6 +10,8 @@ helpviewer_keywords:
 - DoNotExposeGenericLists
 author: gewarren
 ms.author: gewarren
+dev_langs:
+  - CSharp
 ---
 # CA1002: Do not expose generic lists
 
@@ -45,6 +47,10 @@ By default, this rule only looks at externally visible types, but this is [confi
 
 To fix a violation of this rule, change the <xref:System.Collections.Generic.List%601?displayProperty=fullName> type to one of the generic collections that's designed for inheritance.
 
+## Example
+
+:::code language="csharp" source="snippets/csharp/all-rules/ca1002.cs" id="snippet1":::
+
 ## When to suppress warnings
 
 Do not suppress a warning from this rule unless the assembly that raises this warning is not meant to be a reusable library. For example, it would be safe to suppress this warning in a performance-tuned application where a performance benefit was gained from the use of generic lists.

docs/fundamentals/code-analysis/quality-rules/snippets/csharp/all-rules/ca1002.cs

@@ -0,0 +1,32 @@
+using System.Collections.Generic;
+
+namespace ca1001
+{
+    //<snippet1>
+    // This class violates the rule.
+    public class MutableItems
+    {
+        // CA1002: Change 'List<string>' in 'MutableItems.Items' to
+        // use 'Collection<T>', 'ReadOnlyCollection<T>' or 'KeyedCollection<K,V>'.
+        public List<string> Items { get; } = new List<string>();
+
+        public void Add(string item)
+        {
+            Items.Add(item);
+        }
+    }
+
+    // This class satisfies the rule.
+    public class ReadOnlyItems
+    {
+        private readonly List<string> _items = new List<string>();
+
+        public IReadOnlyCollection<string> Items => _items.AsReadOnly();
+
+        public void Add(string item)
+        {
+            _items.Add(item);
+        }
+    }
+    //</snippet1>
+}