Update readme

Author: toyowata

README.md

@@ -24,6 +24,7 @@ Board                          |  Connectivity     | Storage for credentials and
 `Ublox UBLOX_C030_U201`             | Cellular          | SD card                 | Build-only
 `Ublox UBLOX_C030_R412M`            | Cellular          | SD card                 | Build-only
 `Embedded Planet EP_AGORA`          | Cellular          | SPIF                    | Build-only
+`Seeed ARCH_MAX`                    | Ethernet          | SD card                 | Build-only
 
 Build-only = This target is currently verified only via compilation, and is not verified at runtime.