[docs] Make walkthrough and starting Ray materials clear (#7099)

* make starting ray a separate page

* concept

* Apply suggestions from code review

Co-Authored-By: Edward Oakes <ed.nmi.oakes@gmail.com>

* more fics

* Apply suggestions from code review

Co-Authored-By: Edward Oakes <ed.nmi.oakes@gmail.com>

Co-authored-by: Edward Oakes <ed.nmi.oakes@gmail.com>

doc/source/using-ray.rst

@@ -3,14 +3,14 @@ Using Ray
 
 If you’re brand new to Ray, we recommend starting with our `tutorials <https://github.com/ray-project/tutorial>`_.
 
-Below, you'll find information ranging from beginner material (like our `walkthrough <walkthrough.html>`_) to `advanced usage <advanced.html>`_. There are also detailed instructions on how to work with Ray concepts such as Actors and managing GPUs.
+Below, you'll find information ranging from how to `start Ray <starting-ray.html>`_ to `advanced usage <advanced.html>`_. There are also detailed instructions on how to work with Ray concepts such as Actors and managing GPUs.
 
 Finally, we've also included some content on using core Ray APIs with `Tensorflow <using-ray-with-tensorflow.html>`_ and `PyTorch <using-ray-with-pytorch.html>`_.
 
 .. toctree::
    :maxdepth: -1
 
-   walkthrough.rst
+   starting-ray.rst
    actors.rst
    using-ray-with-gpus.rst
    serialization.rst