pybricks.robotics.DriveBase: Add clarifying comments.

Fixes pybricks/support#698

doc/main/robotics.rst

@@ -52,13 +52,20 @@
 
     .. automethod:: pybricks.robotics.DriveBase.stalled
 
+    .. _measuring:
+
     .. rubric:: Measuring and validating the robot dimensions
 
     As a first estimate, you can measure the ``wheel_diameter`` and the
     ``axle_track`` with a ruler. Because it is hard to see where the wheels
     effectively touch the ground, you can estimate the ``axle_track`` as
     the distance between the midpoint of the wheels.
 
+    If you don't have a ruler, you can use a LEGO beam to measure. The
+    center-to-center distance of the holes is 8 mm. For some tyres, the
+    diameter is printed on the side. For example, 62.4 x 20 means that the
+    diameter is 62.4mm and that the width is 20 mm.
+
     In practice, most wheels compress slightly under the weight of your robot.
     To verify, make your robot drive 1000 mm using ``my_robot.straight(1000)``
     and measure how far it really traveled. Compensate as follows:

src/pybricks/robotics.py

@@ -28,8 +28,12 @@ class DriveBase:
 
     **Positive** angles and turn rates mean turning **right**.
     **Negative** means **left**. So when viewed from the top,
-    positive means clockwise and negative means counterclockwise.
+    positive means clockwise and negative means counterclockwise. If desired,
+    you can flip this convention by reversing the ``left_motor`` and
+    ``right_motor`` when you initialize this class.
 
+    See the `measuring`_ section for tips to measure and adjust the diameter
+    and axle track values.
     """
 
     distance_control = _common.Control()
@@ -139,6 +143,10 @@ def settings(self, *args):
 
         If you give no arguments, this returns the current values as a tuple.
 
+        The default values are automatically configured based on your wheel
+        diameter and axle track. They are selected such that your robot
+        drives at about 40% of its maximum speed.
+
         Arguments:
             straight_speed (Number, mm/s): Straight-line speed of the robot.
             straight_acceleration (Number, mm/s²): Straight-line