esp32/boards: Add specific deploy instructions for S3 variant.

Signed-off-by: Damien George <damien@micropython.org>

ports/esp32/boards/GENERIC_S3/board.json

@@ -1,6 +1,6 @@
 {
     "deploy": [
-        "../deploy.md"
+        "../deploy_s3.md"
     ],
     "docs": "",
     "features": [

ports/esp32/boards/GENERIC_S3_SPIRAM/board.json

@@ -1,6 +1,6 @@
 {
     "deploy": [
-        "../deploy.md"
+        "../deploy_s3.md"
     ],
     "docs": "",
     "features": [

ports/esp32/boards/deploy_s3.md

@@ -0,0 +1,14 @@
+Program your board using the esptool.py program, found [here](https://github.com/espressif/esptool).
+
+If you are putting MicroPython on your board for the first time then you should
+first erase the entire flash using:
+
+```bash
+esptool.py --chip esp32s3 --port /dev/ttyACM0 erase_flash
+```
+
+From then on program the firmware starting at address 0:
+
+```bash
+esptool.py --chip esp32s3 --port /dev/ttyACM0 write_flash -z 0 board-20210902-v1.17.bin
+```