doc: issue2551415 correct doc for change input->input_payload in 2.5 the rest interface changed a variable name from input to input_payload. An earlier commit changed the rest docs. This commit adds an item for it to the upgrading 2.4.0->2.5.0 section. Also cross reference added to the rest docs with the updated examples.

try:
    # Python 3+
    from time import perf_counter
except (ImportError, AttributeError):
    # Python 2.5-2.7
    from time import clock as perf_counter  # noqa: F401