Apply suggestions from code review

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: ZeroIntensity

peps/pep-0828.rst

@@ -77,7 +77,7 @@ Implementation complexity has gone down
 Historically, ``yield from`` was not added to asynchronous generators due to
 concerns about the complexity of the implementation. To quote :pep:`525`:
 
-    While it is theoretically possible to implement yield from support for
+    While it is theoretically possible to implement ``yield from`` support for
     asynchronous generators, it would require a serious redesign of the
     generators implementation.
 
@@ -105,7 +105,7 @@ in asynchronous generators:
 3. https://discuss.python.org/t/66886
 
 Additionally, this design decision has `come up
-<https://stackoverflow.com/questions/47376408>`__ on StackOverflow.
+<https://stackoverflow.com/questions/47376408>`__ on Stack Overflow.
 
 
 Subgenerator delegation is useful for asynchronous generators
@@ -146,7 +146,7 @@ Grammar changes
 The ``yield_expr`` and ``simple_stmt`` rules need to be updated for the new
 ``async yield from`` syntax:
 
-.. code-block::
+.. code-block:: peg
 
     yield_expr[expr_ty]:
         | 'async' 'yield' 'from' a=expression