README: add k3-pico-itx MACHINE

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>

Author: threexc

README.md

@@ -41,6 +41,7 @@ This layer depends on:
 | beaglev-starlight-jh7100 | [BeagleV](https://old.beagleboard.org/static/beagleV/beagleV.html)                                           | No longer produced                                                               |
 | eswin-ebc77              | ESWIN EBC77                                                                                                  | Vendor kernel. Use `eswin-ebc77-mainline` for upstream version                   |
 | eswin-ebc77-mainline     | ESWIN EBC77                                                                                                  |                                                                                  |
+| k3-pico-itx              | [Sipeed K3 Pico-ITX](https://sipeed.com/k3)                                                                  | Vendor Kernel                                                                    |
 | freedom-u540             | [HiFive Unleashed](https://www.sifive.com/boards/hifive-unleashed)                                           | Discontinued                                                                     |
 | mangopi-mq-pro           | [MangoPi MQ Pro](https://mangopi.org/mangopi_mqpro)                                                          |                                                                                  |
 | milkv-duo                | [Milk-V Duo](https://milkv.io/duo)                                                                           |                                                                                  |