[doc] Add a note about direnv usage

doc/install.rst

@@ -49,6 +49,17 @@ Choose the relevant tab for details on each of those installation paths.
       with sources is used.  If you'd like to update the lock-file to the
       latest set of compatible dependencies, remove that option.
 
+      If you use `direnv to setup your pixi environment
+      <https://pixi.sh/latest/features/environment/#using-pixi-with-direnv>`_
+      when you enter the directory containing this package, you can use a
+      ``.envrc`` file similar to this:
+
+      .. code:: sh
+
+         watch_file pixi.lock
+         export PIXI_FROZEN="true"
+         eval "$(pixi shell-hook)"
+
 
 .. tab:: CUDA