SKR 1.3 support

[regal niche]

Hi. I am trying to add config for BTT SKR v1.3 + tmc2208 into RatOS 2, but whenever I add board definition, I see this:
board_definition:

    "$schema": "../board-definition.schema.json",
    "name": "SKR v1.3",
    "manufacturer": "BIGTREETECH",
    "serialPath": "/dev/btt-skr-13",
    "firmwareBinaryName": "firmware-btt-skr-13.bin",
    "compileScript": "compile.sh",
    "flashScript": "flash.sh",
    "flashInstructions": "Flashing only works if there's a properly formatted (FAT16 or FAT32 with a small blocksize) micro SD card in the SKR Pro's SD Card slot. The smaller the SD card the better, a cheap 128mb TF-card is perfect.",
}```

Also, I will really appreciate suggestions, where I should make changes in RatOS, to make skr 1.3 as compatible as possible, so in future I can make an PR and by that help someone else who would decide to build V-Core with SKR 1.3 as controller.

[twin mortar]

You're missing documentationLink see the json schema

Your editor (if you're using vscode for example) should tell you exactly what's wrong.