Library needs simpletest example

[kattni]

This library has no simpletest example. This was discussed in #12 but it did not result in the addition of a simpletest. I'm opening a new issue to being this discussion up again.

@jerryneedell or @brentru Do you have any suggestions?

[brentru]

@kattni The example which flashes nina-fw to an esp32 would be a good simpletest -> https://github.com/adafruit/Adafruit_CircuitPython_miniesptool/blob/master/examples/miniesptool_esp32nina.py

[kattni]

@brentru Thank you so much!

[kattni]

@brentru Would you suggest calling it miniesptool_simpletest or miniesptool_esls32nina_simpletest ?

[brentru]

@kattni miniesptool_simpletest is OK