config: Complete pin documentation and experimental probe notes

Add comprehensive technical documentation:
- Complete confirmed pin assignments list for all functions
- Detailed unidentified pins list for future development
- Honest experimental warnings for probe functionality
- Available pins for custom modifications
- Developer notes for future investigation

This provides complete hardware reference for CR-10 Smart CR-FDM v2.5.S1
enabling both reliable operation and future development work.

Signed-off-by: Matias Canosa <matiascanosa@users.noreply.github.com>

config/printer-creality-cr10-smart-cr-fdm-v2.5.s1-2022.cfg

@@ -133,6 +133,15 @@ enable_force_move: True
 # - Main board interface: 2x7 pin (14-pin) + 2x8 pin (16-pin) connectors
 # - Pin 1 identification: Square pad on PCB, remaining pins are circular
 #
+# CONFIRMED PIN ASSIGNMENTS (STM32F103RET6 main board):
+# Motors: PB3,PB4 (Z), PB5,PB6 (Y), PB7,PB8 (X), PB9,PC2 (E), PC3 (Enable)
+# Endstops: PC4 (X), PC5 (Y), PB2 (Z-physical)
+# Heaters: PB13 (Bed), PB14 (Hotend)
+# Thermistors: PB0 (Bed), PB1 (Hotend)  
+# Fans/Outputs: PB15 (Part fan), PC13 (Lights), PA0 (Power)
+# Sensors: PA7 (Filament sensor)
+# Communication: PA9,PA10 (USART1 to host)
+#
 # CONNECTOR 1 - 2x8 (16-pin) - HOTEND & COOLING:
 # Pin 1: HT+, Pin 2: HT+, Pin 3: HT-, Pin 4: TH (Thermistor)
 # Pin 5: Fan/LED VCC, Pin 6: Layer Fan Signal, Pin 7: STM Pin 10, Pin 8: LED Signal
@@ -142,20 +151,42 @@ enable_force_move: True
 # Pin 1-2: Xd/Xb (X Motor), Pin 3-4: Ed/Eb (Extruder), Pin 5-6: X-/FilSensor
 # Pin 7-8: GND, Pin 9: FilRunout, Pin 10: X-, Pin 11-12: Ea/Ec, Pin 13-14: Xa/Xc
 #
-# Known probe pins when enabled: PA4 (probe signal), PA5 (tare control)
+# Probe pins (UNCONFIRMED): PA4 (probe signal?), PA5 (tare control?)
+# WARNING: Pin assignments are speculative based on available pins only
+# Strain gauge probe communication protocol completely unknown
+# PA4/PA5 chosen because they are freed when probe is disabled, but actual
+# probe pins may be different or require secondary board firmware modifications
 # Communication with main board via dedicated pins (not USART1)
+#
+# STM32F103RET6 pins NOT identified in this configuration:
+# Available for future investigation or custom modifications:
+# PA1, PA2, PA3, PA6, PA8, PA11, PA12, PA15
+# PB0 (bed thermistor - could be repurposed if bed sensor moved)
+# PB1 (hotend thermistor - could be repurposed if sensor moved)  
+# PC0, PC1, PC6, PC7, PC8, PC9, PC10, PC11, PC12, PC14, PC15
+# PD0, PD1 (if available on this package)
+#
+# Notes for developers:
+# - PA9/PA10: Reserved for USART1 (host communication)
+# - PA4/PA5: Suspected probe/tare pins (unconfirmed)
+# - Some pins may be connected to secondary board connectors
+# - Verify pin availability before use in custom configurations
 
 # Optional: Probe configuration (commented out for Z endstop operation)
-# Before using probe, comment out the stepper_z endstop_pin above
-# and uncomment the probe section below
+# EXPERIMENTAL: Strain gauge probe functionality completely unverified
+# Pin assignments below are speculative and likely incorrect
+# No successful probe operation achieved - use physical Z endstop for reliability
+# Before attempting probe, comment out the stepper_z endstop_pin above
+# and uncomment the probe section below (expect failures)
 #[probe]
-#pin: ~PA4
+#pin: ~PA4  # UNCONFIRMED: May not be correct pin
 #z_offset: -0.75
 #samples: 2
 
 # Optional: Probe tare pin (used with probe configuration above)
+# EXPERIMENTAL: Pin assignment unconfirmed, functionality unknown
 #[output_pin PROBE_TARE_PIN]
-#pin: PA5
+#pin: PA5  # UNCONFIRMED: May not be correct pin
 #value: 0
 
 # Optional: Safe Z homing (used with probe configuration above)