[BOARD/README] Firstboot flashing_procedure-v2 (#42)

* [FIRSTBOOT] refactor code:
 -auto-detect all possible variants in firstboot
- DRY script code
- add $RESIZE_COMMENCED , $BITTBOY_CONFIG , $MIYOO_CONFIGvariable
- add debug log before any shutdown
- don't `export` env var if not needed
- move and use $DETECTED auto_ID variants on II Test_Block
- cleanup + add more descriptions
- add Test_Flip prompt for double check on Test Video (only if enduser selected "Flipped!" at first test)
- remove useless SWAP & MAIN part. mount
- add safety read-only for /boot before shutdown

* [BOARD] add gmenu2x inputs inputs with `manifest`
- update genimage config with `input_bittboy.conf` and `input_miyoo.conf`

* [README] Add flashing procedure schematic (made in draw.io)

board/miyoo/genimage-sdcard.cfg

@@ -17,6 +17,12 @@ image bootfs.vfat {
 		file configs/manifest {
 			image = "boot/configs/manifest"
 		}
+		file configs/input_bittboy.conf {
+			image = "boot/configs/input_bittboy.conf"
+		}
+		file configs/input_miyoo.conf {
+			image = "boot/configs/input_miyoo.conf"
+		}
 		file configs/.volume.conf {
 			image = "boot/configs/.volume.conf"
 		}
@@ -74,4 +80,4 @@ image ${IMAGE_NAME:-miyoo-cfw-2.0.0.img} {
 		bootable = "false"
 		image = "mainfs.vfat"
 	}
-}
+}