[doc] updated installation process with second conda channel

Closes #156

doc/install.rst

@@ -60,9 +60,10 @@ Installation Steps
 ------------------
 
 #. Activate the Conda environment you will be adding ``beat.editor`` to
-#. Add a new Conda channel: ::
+#. Add two new Conda channels: ::
 
    $ conda config --env --add channels https://www.idiap.ch/software/beat/conda/label/beta
+   $ conda config --env --add channels https://www.idiap.ch/software/beat/conda
 
 #. Install the ``beat.editor`` package: ::