improve ext readme

include/vclib/ext/README.md

@@ -1,14 +1,14 @@
-# External Library Support
+# External Libraries
 
 This folder contains a set of VCLib functions and classes that can be used only if you have the corresponding external library available on your system.
 
 The functionalities are then accessible under a specific namespace for each library.
 
-A list of the supported libraries and their namespaces is provided below:
+A list of the supported libraries, their paths and their namespaces is provided below:
 
-| Library(s) | Namespace | Notes |
-|:-------:|:---------:|:-----:|
-| [OpenGL2](https://registry.khronos.org/OpenGL-Refpages/gl2.1/) | `vcl::gl2` | |
-| [Qt6](https://www.qt.io/) | `vcl::qt` | |
-| [QGLViewer](http://libqglviewer.com/) | `vcl::qgl` | This library requires Qt6 |
-| [VCG](http://vcg.isti.cnr.it/vcglib/) | `vcl::vc` | |
+| Library(s) | Namespace | Path | Notes |
+|:----------:|:---------:|:----:|:-----:|
+| [OpenGL 2.1](https://registry.khronos.org/OpenGL-Refpages/gl2.1/) | `vcl::gl2` | `ext/opengl2` | |
+| [Qt 6](https://www.qt.io/) | `vcl::qt` | `ext/qt` | |
+| [QGLViewer](http://libqglviewer.com/) | `vcl::qgl` | `ext/qglviewer` | This library requires Qt6 |
+| [VCG](http://vcg.isti.cnr.it/vcglib/) | `vcl::vc` | `ext/vcg` | |