docs/library/builtins.rst: Add module title.
docs/library/builtins.rst: Add module title.

This fixes the rendering on library/index.rst.

Signed-off-by: Jim Mussared <e84f5c941266186d0c97dcc873413469b954847e@gmail.com>

bvernoux/micropython,adafruit/circuitpython,bvernoux/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,bvernoux/micropython,adafruit/circuitpython,bvernoux/micropython,adafruit/circuitpython,bvernoux/micropython