Fix note on indexed draw parameters

Author: SaschaWillems

en/04_Vertex_buffers/03_Index_buffer.adoc

@@ -144,7 +144,7 @@ The first two parameters specify the number of indices and the number of instanc
 We're not using instancing, so just specify `1` instance.
 The number of indices represents the number of vertices that will be passed to the vertex shader.
 The next parameter specifies an offset into the index buffer, using a value of `1` would cause the graphics card to start reading at the second index.
-The second to last parameter specifies an offset to add to the indices in the index buffer.
+The second to last parameter specifies an offset to add to the vertex index before indexing into the vertex buffer.
 The final parameter specifies an offset for instancing, which we're not using.
 
 Now run your program and you should see the following: