PEP 523: Fix Sphinx reference warnings (#4777)

Author: SpecLad

peps/pep-0523.rst

@@ -239,11 +239,11 @@ implementing their own JITs for CPython by utilizing the proposed API.
 Other JITs
 ''''''''''
 
-It should be mentioned that the Pyston team was consulted on an
+It should be mentioned that the Pyston [#pyston]_ team was consulted on an
 earlier version of this PEP that was more JIT-specific and they were
 not interested in utilizing the changes proposed because they want
 control over memory layout they had no interest in directly supporting
-CPython itself. An informal discussion with a developer on the PyPy
+CPython itself. An informal discussion with a developer on the PyPy [#pypy]_
 team led to a similar comment.
 
 Numba [#numba]_, on the other hand, suggested that they would be