[doc] Add command pip install of new cube

doc/tutorials/base/customizing-the-application.rst

@@ -24,6 +24,11 @@ cube::
 This will create a a directory named :file:`cubicweb-myblog` reflecting the
 structure described in :ref:`cubelayout`.
 
+To install your new cube on the virtual environment, run in
+the :file:`cubicweb-myblog` directory::
+
+  pip install -e .
+
 All `cubicweb-ctl` commands are described in details in
 :ref:`cubicweb-ctl`.