Fix typo: missing 'install'. (#78448)

docs/docsite/rst/dev_guide/developing_collections_documenting.rst

@@ -23,7 +23,7 @@ You can use `antsibull-docs <https://pypi.org/project/antsibull-docs>`_ to build
 
 #. Create your collection and make sure you can use it with ansible-core by adding it to your :ref:`COLLECTIONS_PATHS`.
 #. Create a directory ``dest`` and run ``antsibull-docs sphinx-init --use-current --dest-dir dest namespace.name``, where ``namespace.name`` is the name of your collection.
-#. Go into ``dest`` and run ``pip -r requirements.txt``. You might want to create a venv and activate it first to avoid installing this globally.
+#. Go into ``dest`` and run ``pip install -r requirements.txt``. You might want to create a venv and activate it first to avoid installing this globally.
 #. Then run ``./build.sh``.
 #. Open ``build/html/index.html`` in a browser of your choice.