Docs: make a tutorial example more precise (#125066)

Based on discussion here:

https://discuss.python.org/t/omission-in-the-documentation/66816

Author: nedbat

Doc/tutorial/introduction.rst

@@ -197,21 +197,19 @@ and workarounds.
 String literals can span multiple lines.  One way is using triple-quotes:
 ``"""..."""`` or ``'''...'''``.  End of lines are automatically
 included in the string, but it's possible to prevent this by adding a ``\`` at
-the end of the line.  The following example::
-
-   print("""\
+the end of the line.  In the following example, the initial newline is not
+included::
+
+   >>> print("""\
+   ... Usage: thingy [OPTIONS]
+   ...      -h                        Display this usage message
+   ...      -H hostname               Hostname to connect to
+   ... """)
    Usage: thingy [OPTIONS]
         -h                        Display this usage message
         -H hostname               Hostname to connect to
-   """)
-
-produces the following output (note that the initial newline is not included):
 
-.. code-block:: text
-
-   Usage: thingy [OPTIONS]
-        -h                        Display this usage message
-        -H hostname               Hostname to connect to
+   >>>
 
 Strings can be concatenated (glued together) with the ``+`` operator, and
 repeated with ``*``::