Grammar corrections in abc.rst (GH-10525)

(cherry picked from commit 8e0b05e)

Co-authored-by: Andrés Delfino <[email protected]>

Author: miss-islington

Doc/library/abc.rst

@@ -18,10 +18,10 @@ see the PEP for why this was added to Python. (See also :pep:`3141` and the
 :mod:`numbers` module regarding a type hierarchy for numbers based on ABCs.)
 
 The :mod:`collections` module has some concrete classes that derive from
-ABCs; these can, of course, be further derived. In addition the
+ABCs; these can, of course, be further derived. In addition, the
 :mod:`collections.abc` submodule has some ABCs that can be used to test whether
-a class or instance provides a particular interface, for example, is it
-hashable or a mapping.
+a class or instance provides a particular interface, for example, if it is
+hashable or if it is a mapping.
 
 
 This module provides the metaclass :class:`ABCMeta` for defining ABCs and