Add issue template file

[brainelectronics]

Fill existing contribution markdown file in the docs folder with content.

Also add an issues and PR template file

[brainelectronics]

Every issue should be reported with the used version of this lib and steps to reproduce the issue, e.g.

• MicroPython board (RP2, pyboard, ESP32, ESP8266, Unix)
• MicroPython version

import os
from umodbus import version

print("MicroPython infos: {}".format(os.uname()))
print("Used micropthon-modbus version: {}".format(version.__version__))
# Used MicroPython infos: (...)
# Used micropython-modbus version: 2.1.0-rc15.dev39