signaltypes: Bare minimal async docs.

This is nowhere near complete, but provides handles to start documenting async for the relevant methods.

examples/pup/robotics/drivebase_async.py

@@ -0,0 +1,27 @@
+from pybricks.pupdevices import Motor
+from pybricks.parameters import Direction, Port
+from pybricks.robotics import DriveBase
+from pybricks.tools import multitask, run_task
+
+# Set up all devices.
+left = Motor(Port.A, Direction.COUNTERCLOCKWISE)
+right = Motor(Port.B)
+gripper = Motor(Port.C)
+drive_base = DriveBase(left, right, 56, 114)
+
+
+# Move the gripper up and down.
+async def move_gripper():
+    await gripper.run_angle(500, -90)
+    await gripper.run_angle(500, 90)
+
+
+# Drive forward, turn move gripper at the same time, and drive backward.
+async def main():
+    await drive_base.straight(250)
+    await multitask(drive_base.turn(90), move_gripper())
+    await drive_base.straight(-250)
+
+
+# Runs the main program from start to finish.
+run_task(main())