Add pinout documentation

prototype/esp32/README.md

@@ -5,6 +5,11 @@ Feel free to change any options in the Makefile to help it work for your system.
 For example, where the Arduino libraries are held, the connecting baud rate, etc.
 Should work by default in most distributions.
 
+## Pinout
+
+The board used in this project has a unique pin layout that isn't very common.
+The pin layout has been documented in the `pinout` directory both in image and markdown form.
+
 ## Installing Dependencies
 
 To install the dependencies for the board, use the `make install-deps` command.