improved slightly the installation documentation

doc/installation.rst

@@ -5,7 +5,7 @@ Installation
 
   * Using Git, sources can be retrived with the following command ::
 
-      git clone https://gitlab.esrf.fr/mirone/XRStools
+      git clone https://gitlab.esrf.fr/ixstools/xrstools
 
   * for a local installation you can use  ::
 
@@ -17,11 +17,28 @@ Installation
 	export PATH=/home/yourname/bin:$PATH
 
 
-  * For the roi selection tool you need a recent version of pymca installed on your sistem
+  * To install by creating a virtual environment ::
 
+      export MYPREFIX=/REPLACE/WITH/YOUR/TARGET
+      cd ${MYPREFIX}
+      python3 -m venv myenv
 
   * Examples :
         There is an archive containing datas for tests by anonymous ftp at ::
 
-	  http://ftp.esrf.fr/pub/scisoft/___STILL_TO_BE_PLACED
+      source ${MYPREFIX}/myenv/bin/activate
+      pip install pip --upgrade
+      pip install setuptools --upgrade
+
+      git clone https://gitlab.esrf.fr/ixstools/xrstools
+
+      cd ${MYPREFIX}/xrdctpc/
+      pip install -r requirements.txt
+      python setup.py install
+
+  * For the roi selection tool you need a recent version of pymca installed on your sistem
+
+
+  * Usage examples can be found in the non regression directory.
+