Add C# Example to ImmediateMesh.xml

doc/classes/ImmediateMesh.xml

@@ -15,6 +15,14 @@
 		mesh.surface_add_vertex(Vector3.ZERO)
 		mesh.surface_end()
 		[/gdscript]
+		[csharp]
+		var mesh = new ImmediateMesh();
+		mesh.SurfaceBegin(Mesh.PrimitiveType.Triangles);
+		mesh.SurfaceAddVertex(Vector3.Left);
+		mesh.SurfaceAddVertex(Vector3.Forward);
+		mesh.SurfaceAddVertex(Vector3.Zero);
+		mesh.SurfaceEnd();
+		[/csharp]
 		[/codeblocks]
 		[b]Note:[/b] Generating complex geometries with [ImmediateMesh] is highly inefficient. Instead, it is designed to generate simple geometry that changes often.
 	</description>