bpo-35835: Add reference to Python 3.7 new breakpoint() function in pdb documentation. (GH-11691)

Doc/library/pdb.rst

@@ -76,6 +76,10 @@ at the location you want to break into the debugger.  You can then step through
 the code following this statement, and continue running without the debugger
 using the :pdbcmd:`continue` command.
 
+.. versionadded:: 3.7
+   The built-in :func:`breakpoint()`, when called with defaults, can be used
+   instead of ``import pdb; pdb.set_trace()``.
+
 The typical usage to inspect a crashed program is::
 
    >>> import pdb