esp32/README: Add troubleshooting section to the end.

MrSurly · dpgeorge · commit a5439a1830e1 · 2017-03-31T22:42:02.000+11:00
diff --git a/esp32/README.md b/esp32/README.md
@@ -159,3 +159,10 @@ boot.py file):
 import machine
 antenna = machine.Pin(16, machine.Pin.OUT, value=0)
 ```
+
+Troubleshooting
+---------------
+
+* Continuous reboots after programming: Ensure FLASH_MODE is correct for your
+  board (e.g. ESP-WROOM-32 should be DIO). Then perform a `make clean`, rebuild,
+  redeploy.
