Issue #26462: Doc: avoid literal_block warnings, fix syntax highlighting.

Patch by Julien Palard.
diff --git a/Doc/tutorial/interpreter.rst b/Doc/tutorial/interpreter.rst
index 5f37504..50e50c7 100644
--- a/Doc/tutorial/interpreter.rst
+++ b/Doc/tutorial/interpreter.rst
@@ -93,7 +93,9 @@
 usually three greater-than signs (``>>>``); for continuation lines it prompts
 with the *secondary prompt*, by default three dots (``...``). The interpreter
 prints a welcome message stating its version number and a copyright notice
-before printing the first prompt::
+before printing the first prompt:
+
+.. code-block:: shell-session
 
    python
    Python 2.7 (#1, Feb 28 2010, 00:02:06)