Add the link toward the dictionary of variables

docs/index.md

@@ -8,6 +8,8 @@ See [user manual](usermanual.md) first for details
 
 You can also [use the demonstrator tool on line](http://apidemo.portic.fr/)
 
+Note that all fields are fully documented in [a tabular file - CSV -  on the GITLAB](https://gitlab.huma-num.fr/portic/porticapi/-/raw/master/static/data/api_portic.csv) : name of the field, definition, exemple. 
+
 <!--  ![Pointcalls API - Results, and download time](img/temps_telechargement.png) -->
 
 Licence : [![AGPLv3.png](http://www.gnu.org/graphics/agplv3-with-text-162x68.png)](agpl-3.0.md)