Patch for #834

[2bndy5]

solves #834

Using the RPi OS lite image doesn't ship with pigpio, and the configure script wasn't properly detecting if pigpio is installed.

• adjust configure script to check for pigpio in
  1. user installed location (when fetched from git src - typically in /usr/local/lib)
  2. apt installed location (typically in /usr/lib)
  3. and /usr/arm-linux-gnueabihf (for 32bit cross-compiling purposes)
• adjust Makefile for lib and linux examples
• augment install docs with info about pigpio as req for IRQ (and remind reader that RPi OS lite doesn't come with pigpio).

I tested this with the Linux CI: When using the SPIDEV driver (with the configure script), pigpio is no longer installed.