Add back numpy v2 warning.

docs/getting_started.in.rst

@@ -50,14 +50,24 @@ Pip (PyPI)
     pip install open3d        # or
     pip install open3d-cpu    # Smaller CPU only wheel on x86_64 Linux (since v0.17+)
 
+.. warning::
+
+   Versions of ``numpy>=2.0.0`` require ``Open3D>0.18.0`` or the latest development
+   version of Open3D. If you are using an older version of Open3D, downgrade ``numpy`` 
+   with
+
+   .. code-block:: bash
+
+        pip install "numpy<2.0.0"
+
 .. warning::
 
    Please upgrade your ``pip`` to a version >=20.3 to install Open3D in Linux,
    e.g. with
 
    .. code-block:: bash
 
-        pip install -U pip>=20.3
+        pip install -U "pip>=20.3"
 
 .. note::
     In general, we recommend using a