Update README.md

README.md

@@ -27,8 +27,9 @@ Most of these modulea are installed by default
 All the other modules are optional have dependencies
 
 - [gnuplot](https://promethe.u-cergy.fr/blaar/gnuplot.git) Allows to make graphs from data of blc_channels (require gnuplot)
-- [png](https://promethe.u-cergy.fr/blaar/png.git)
-- [sndfile](https://promethe.u-cergy.fr/blaar/sndfile.git)
+- [gtk](https://promethe.u-cergy.fr/blaar/gtk.git) Provides a graphical user interface. For now, it displays images.
+- [png](https://promethe.u-cergy.fr/blaar/png.git) Saves and loads png images.
+- [sndfile](https://promethe.u-cergy.fr/blaar/sndfile.git) Reads and writes sound files in with many sound formats. 
 
 Specific Linux
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