Correct directory to include new `ports` layer

Board-Teensy-3.1-3.5-3.6.md

@@ -45,7 +45,7 @@ To build, you can either use the ARM toolchain from [here](https://launchpad.net
 
 ```
 git clone https://github.com/micropython/micropython
-cd micropython/teensy
+cd micropython/ports/teensy
 make BOARD=TEENSY_3.1
 ```
 BOARD can be one of TEENSY_3.1, TEENSY_3.5, or TEENSY_3.6. If no BOARD is specified, then TEENSY_3.1 will be assumed.