Fix "Python" casing in a few places (GH-9001)

Doc/howto/descriptor.rst

@@ -11,7 +11,7 @@ Abstract
 --------
 
 Defines descriptors, summarizes the protocol, and shows how descriptors are
-called.  Examines a custom descriptor and several built-in python descriptors
+called.  Examines a custom descriptor and several built-in Python descriptors
 including functions, properties, static methods, and class methods.  Shows how
 each works by giving a pure Python equivalent and a sample application.
 
@@ -275,7 +275,7 @@ variable name.
 To support method calls, functions include the :meth:`__get__` method for
 binding methods during attribute access.  This means that all functions are
 non-data descriptors which return bound methods when they are invoked from an
-object.  In pure python, it works like this::
+object.  In pure Python, it works like this::
 
     class Function(object):
         . . .

Doc/howto/instrumentation.rst

@@ -369,13 +369,13 @@ available:
 .. c:function:: python.function.entry(str filename, str funcname, int lineno, frameptr)
 
    This probe point indicates that execution of a Python function has begun.
-   It is only triggered for pure-python (bytecode) functions.
+   It is only triggered for pure-Python (bytecode) functions.
 
 .. c:function:: python.function.return(str filename, str funcname, int lineno, frameptr)
 
    This probe point is the converse of :c:func:`python.function.return`, and
    indicates that execution of a Python function has ended (either via
-   ``return``, or via an exception).  It is only triggered for pure-python
+   ``return``, or via an exception).  It is only triggered for pure-Python
    (bytecode) functions.