Expand documentation to clarify pin notation and Servo usage (#2326)

docs/digital.rst

@@ -6,6 +6,10 @@ Board-Specific Pins
 The Raspberry Pi Pico RP2040 chip supports up to 30 digital I/O pins,
 however not all boards provide access to all pins.
 
+Pin Notation
+------------
+When using Analog or Digital I/Os, if you supply an integer it specifies the RP2040 GPIO pin to use. Using Dx or Ax notation (for example, D4 or A3) may be necessary on boards without a direct PCB pin to GPIO mapping.
+
 Input Modes
 -----------
 The Raspberry Pi Pico has 3 Input modes settings for use with `pinMode`: `INPUT`, `INPUT_PULLUP` and `INPUT_PULLDOWN`

docs/servo.rst

@@ -11,3 +11,10 @@ require the use of a PIO machine.
 See the Arduino standard
 `Servo documentation <https://www.arduino.cc/reference/en/libraries/servo/>`_
 for detailed usage instructions.  There is also an included ``sweep`` example.
+
+Pulse Width Defaults
+--------------------
+The defaults in the Servo library are conservatively set to avoid damage in the case of over-driving. The pulse widths individual servos, especially the no-name or clones, occasionally need tweaking.
+
+You can set the min and max servo pulse width in the attach command, with default values used in most Arduino cores of 540/2400:
+```myServo.attach(D3, 540, 2400)```