Update xml example (#50402)

* Update access-modifiers.md

Added description for file access type modifier

* Add XML documentation for Namespace and Class tags

Author: bigboybamo

docs/csharp/language-reference/xmldoc/recommended-tags.md

@@ -265,6 +265,14 @@ Here's an example showing the difference between `<para>` and `<br/>`:
         <term>Assembly</term>
         <description>The library or executable built from a compilation.</description>
     </item>
+    <item>
+        <term>Namespace</term>
+        <description>A logical grouping of related types such as classes and interfaces.</description>
+    </item>
+    <item>
+        <term>Class</term>
+        <description>A blueprint used to create objects, containing properties and methods.</description>
+    </item>
 </list>
 ```