README: add description

README

 # LBMC module repository
 
-# Installation
+## Description
+
+This repository is the development of the LBMC module repository as
+available on the PSMN in the /Xnfs/site/lbmcdb/communs_data/modules/ folder.
+
+If you don't want to contribute, you don't need to clone this repository and
+you can proceed with the instruction of the **Installation** section.
+
+## Installation
 
 To get access to the LBMC modules repository use the following command:
 
@@ -10,7 +18,7 @@ source /usr/share/modules/init/bash
 module load use.own
 ```
 
-You can add the following line to your `~/.bashrc` file to make this change
+You can add the following lines to your `~/.bashrc` file to make this change
 permanent :
 
 ```sh