mimxrt/boards: Extend the deploy_teensy.md instructions.

ports/mimxrt/boards/deploy_teensy.md

@@ -11,4 +11,9 @@ or for Teensy 4.1:
 teensy_loader_cli --mcu=imxrt1062 -v -w TEENSY41-<date_version_tag>.hex
 ```
 
-When loading the firmware the PJRC boot loader will erase the content of the board file system.
+Instead of imxrt1062 with the --mcu option, you can as well use the board specic names
+TEENSY40, TEENSY41 or TEENSY_MICROMOD. When loading the firmware the PJRC boot loader
+will erase the board file system.
+
+Note: If the Teensy board is equipped with Teensy bootloader v1.07 and up, the first attempt to
+upload the firmware may fail. In that case try again.