Document xiao esp32s3 wiring pins

[jmarler]

problem

The wiring section says the sensor connects to "pins 6 and 7" and the interrupt to "pin 1". Those are XIAO silkscreen labels (d6, d7, d1), but the firmware constants in main/fingerprint.c are GPIO numbers (43, 44, 2), and the two sets look unrelated. Anyone following a build video that uses a different ESP32-S3 board will wire to the wrong pads.

changes

Rewrites the wiring section with an explicit mapping table:

sensor wire	xiao pad	esp32-s3 gpio	firmware constant
sensor tx	d7	gpio44	FP_RX_PIN
sensor rx	d6	gpio43	FP_TX_PIN
touch / interrupt out	d1	gpio2	FP_INT_PIN

Also adds:

• that TX and RX cross over
• physical pad locations relative to the USB-C connector, plus a link to the Seeed pin list
• that FP_INT_PIN is read active high with a pull-down, so the sensor must drive it high on touch
• that some ZW101 modules have a separate touch power pin (vt or 3v3t) and the touch output stays dead without it
• what to change when using a board other than the XIAO

testing

Wired against this table on a XIAO ESP32S3 with a ZW101 sensor. tinytouch status reports sensor=ok, fingerprint enrollment and PIV login both work.