closes pythongh-97650: correct sphinx executable (pythongh-97651)

(cherry picked from commit 0179a82)

Co-authored-by: NoSuck <NoSuck@users.noreply.github.com>

Doc/README.rst

@@ -40,7 +40,7 @@ If you'd like to create the virtual environment in a different location,
 you can specify it using the ``VENVDIR`` variable.
 
 You can also skip creating the virtual environment altogether, in which case
-the Makefile will look for instances of ``sphinxbuild`` and ``blurb``
+the Makefile will look for instances of ``sphinx-build`` and ``blurb``
 installed on your process ``PATH`` (configurable with the ``SPHINXBUILD`` and
 ``BLURB`` variables).