docs: clarify the need for having 'npm' and 'node' available in $PATH

docs/installation.rst

@@ -141,9 +141,13 b' You can now proceed to :ref:`install-fro'
 Prepare front-end files
 -----------------------
 
-Finally, the front-end files must be prepared. This requires ``npm`` version 6
-or later, which needs ``node.js`` (version 12 or later). Prepare the front-end
-by running::
+Finally, the front-end files with CSS and JavaScript must be prepared. This
+depends on having some commands available in the shell search path: ``npm``
+version 6 or later, and ``node.js`` (version 12 or later) available as
+``node``. The installation method for these dependencies varies between
+operating systems and distributions.
+
+Prepare the front-end by running::
 
     kallithea-cli front-end-build
 

docs/overview.rst

@@ -21,8 +21,8 b' 2. **Install Kallithea software.**'
     This makes the ``kallithea-cli`` command line tool available.
 
 3. **Prepare front-end files**
-    Some front-end files must be fetched or created using ``npm`` tooling so
-    they can be served to the client as static files.
+    Some front-end files must be fetched or created using ``npm`` and ``node``
+    tooling so they can be served to the client as static files.
 
 4. **Create low level configuration file.**
     Use ``kallithea-cli config-create`` to create a ``.ini`` file with database