Update installation.rst

doc/chapters/installation.rst

@@ -31,6 +31,14 @@ programme as user.
     git clone https://gitlab.camras.nl/marc/backend.git
     git clone https://gitlab.camras.nl/marc/createpointings.git
 
+On mecury the telescope class is already installed. For other systems the
+class can be installed locally or in system. 
+
+::
+
+    git clone https://gitlab.camras.nl/dijkema/telescope.git
+
+Run python3 setup.py install to install the telescope in system.
 
 Check for each programme if DT Obs can find the proper location. Each class can
 be tested individually if needed.