docs/pycom_esp32/underhood.rst: Minor improvements. Add missing PWM reference.
docs/pycom_esp32/underhood.rst: Minor improvements. Add missing PWM reference.

jmarcelino/pycom-micropython,jmarcelino/pycom-micropython,jmarcelino/pycom-micropython,jmarcelino/pycom-micropython,jmarcelino/pycom-micropython