Document npm

documentation/usage/extension/cotton_candy.rst

@@ -2,6 +2,9 @@ The *Cotton Candy* extension
 ==========================
 The :py:class:`betty.extension.CottonCandy` extension provides Betty's default theme.
 
+.. important::
+    This extension requires :doc:`npm </usage/npm>`.
+
 Enable this extension through Betty Desktop, or in your project's :doc:`configuration file </usage/project/configuration>` as follows:
 
 .. md-tab-set::

documentation/usage/extension/http_api_doc.rst

@@ -3,6 +3,9 @@ The *HTTP API Documentation* extension
 The :py:class:`betty.extension.HttpApiDoc` extension renders interactive and user-friendly HTTP API documentation using
 `ReDoc <https://github.com/Redocly/redoc>`_.
 
+.. important::
+    This extension requires :doc:`npm </usage/npm>`.
+
 Enable this extension through Betty Desktop, or in your project's :doc:`configuration file </usage/project/configuration>` as follows:
 
 .. md-tab-set::

documentation/usage/extension/maps.rst

@@ -3,6 +3,9 @@ The *Maps* extension
 The :py:class:`betty.extension.Maps` extension renders interactive maps using `Leaflet <https://leafletjs.com/>`_ and
 `OpenStreetMap <https://www.openstreetmap.org/>`_.
 
+.. important::
+    This extension requires :doc:`npm </usage/npm>`.
+
 Enable this extension through Betty Desktop, or in your project's :doc:`configuration file </usage/project/configuration>` as follows:
 
 .. md-tab-set::

documentation/usage/extension/trees.rst

@@ -2,6 +2,9 @@ The *Trees* extension
 ===================
 The :py:class:`betty.extension.Trees` extension renders interactive family trees using `Cytoscape.js <http://js.cytoscape.org/>`_.
 
+.. important::
+    This extension requires :doc:`npm </usage/npm>`.
+
 Enable this extension through Betty Desktop, or in your project's :doc:`configuration file </usage/project/configuration>` as follows:
 
 .. md-tab-set::

documentation/usage/npm.rst

@@ -0,0 +1,12 @@
+npm
+===
+
+Some optional parts of Betty use third-party `JavaScript <https://en.wikipedia.org/wiki/JavaScript>`_
+packages to help build your site.
+
+If you installed the :doc:`Betty Desktop application </installation/desktop>`, all necessary components
+are included, and you will not have to take any additional steps.
+
+If you installed Betty :doc:`via pip </installation/pip>` or :doc:`from source </installation/source>`,
+you must also install `Node.js <https://nodejs.org/>`_, which includes npm. Afterwards, ensure ``npm``
+is in your ``PATH``, e.g. that ``npm`` can be run in a terminal from anywhere.