Toolchain setup in ports/esp32/README is out of date

[aykevl]

The README for the esp32 gives this text as part of "Setting up the toolchain and ESP-IDF":

Follow the guide "Setting Up ESP-IDF", for Windows, Mac or Linux. You only need to perform up to "Step 2" of the guide, by which stage you should have installed the cross-compile and cloned the ESP-IDF repository.

Apparently they expect the guide to cover cloning of the repository, but it only gives instructions for how to download a binary toolchain from Espressif. I worked around it by also downloading the esp-idf repository, checking out the right hash and doing a submodule update (without compiling), but I'm not sure whether this is the correct approach. Now I have set ESPIDF to the esp-idf repository and have added the binary toolchain from Espressif to my PATH variable. This works, mostly.

[dpgeorge]

The README was improved upstream in commit micropython/micropython@f16c775