Fix spelling and markup in documentation and code comment

* Mark up ``--help`` to avoid generating an en dash
* Use forward slash in Unix command line with a dollar sign ($) prompt
diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
index 4ce6835..1ea1f3f 100644
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -173,7 +173,7 @@
    * conflict_handler_ - The strategy for resolving conflicting optionals
      (usually unnecessary)
 
-   * add_help_ - Add a -h/--help option to the parser (default: ``True``)
+   * add_help_ - Add a ``-h/--help`` option to the parser (default: ``True``)
 
 The following sections describe how each of these are used.
 
@@ -204,7 +204,7 @@
     -h, --help  show this help message and exit
     --foo FOO   foo help
    $ cd ..
-   $ python subdir\myprogram.py --help
+   $ python subdir/myprogram.py --help
    usage: myprogram.py [-h] [--foo FOO]
 
    optional arguments: