Fix typos in docs (#13956)

Brand new to open source, sure hope this is helpful and that I'm doing
this right.

docs/source/config/extensions/index.rst

@@ -55,10 +55,10 @@ imported, and the currently active :class:`~IPython.core.interactiveshell.Intera
 instance is passed as the only argument. You can do anything you want with
 IPython at that point.
 
-:func:`load_ipython_extension` will not be called again if the user use
-`%load_extension`.  The user have to explicitly ask the extension to be
-reloaded (with `%reload_extension`). In case where the use ask the extension to
-be reloaded, , the extension will be unloaded (with
+:func:`load_ipython_extension` will not be called again if the users use
+`%load_extension`.  The user has to explicitly ask the extension to be
+reloaded (with `%reload_extension`). In cases where the user asks the extension to
+be reloaded, the extension will be unloaded (with
 `unload_ipython_extension`), and loaded again. 
 
 Useful :class:`InteractiveShell` methods include :meth:`~IPython.core.interactiveshell.InteractiveShell.register_magic_function`,