Add T.A.M.I Drawbot modifications changelog to README

- Added changelog section documenting all modifications since forking
- Documented December 4, 2025 changes (inverted servo PWM, M5 fix)
- Listed earlier modifications (servo mode, homing fix)

HOMING_FIX.md

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+# GRBL Homing Issue - Fix Documentation
+
+## Problem Identified
+
+Your GRBL configuration was attempting to home X and Y axes **simultaneously** in `HOMING_CYCLE_1`. When axes home at the same time, whichever limit switch is encountered first can cause the entire homing cycle to abort, especially if:
+
+- Axes have different distances to travel to their limit switches
+- Mechanical tolerances cause one axis to reach its switch before the other
+- The machine isn't perfectly square
+
+## Root Cause
+
+In `grbl/limits.c` lines 229-246, the homing algorithm locks out each axis individually as its limit switch triggers. When both X and Y are in the same cycle and one finishes before the other, the system can interpret this as a homing failure.
+
+## Solution Applied
+
+**Changed in `grbl/config.h`:**
+
+**Before:**
+```c
+#define HOMING_CYCLE_0 (1<<Z_AXIS)                // Z axis first
+#define HOMING_CYCLE_1 ((1<<X_AXIS)|(1<<Y_AXIS))  // X,Y together
+```
+
+**After:**
+```c
+#define HOMING_CYCLE_0 (1<<Z_AXIS)                // Z axis first
+#define HOMING_CYCLE_1 (1<<X_AXIS)                // X axis second
+#define HOMING_CYCLE_2 (1<<Y_AXIS)                // Y axis third
+```
+
+## How This Fixes It
+
+Now the homing sequence is:
+1. **Cycle 0**: Z-axis homes (clears workspace)
+2. **Cycle 1**: X-axis homes independently
+3. **Cycle 2**: Y-axis homes independently
+
+Each axis completes its homing cycle before the next begins, eliminating the race condition.
+
+## Next Steps
+
+1. **Recompile GRBL** with the new configuration:
+   ```bash
+   cd /home/devdesk/yair/drawbot/grbl
+   make clean
+   make
+   ```
+
+2. **Upload to your Arduino/controller**
+
+3. **Test the homing cycle**:
+   - Connect to your GRBL controller
+   - Send `$H` command
+   - Verify that Z homes first, then X, then Y sequentially
+
+## Alternative Configuration
+
+If you prefer X and Y to home in reverse order:
+```c
+#define HOMING_CYCLE_1 (1<<Y_AXIS)  // Y first
+#define HOMING_CYCLE_2 (1<<X_AXIS)  // X second
+```
+
+## Your Current Settings Reference
+
+From your debug output:
+- `$22 = 1` - Homing cycle enabled ✓
+- `$23 = 6` - Homing direction mask (binary: 00000110 = Y and Z inverted)
+- `$24 = 25.000` - Homing feed rate
+- `$25 = 500.000` - Homing seek rate
+- `$26 = 250` - Homing debounce delay
+- `$27 = 1.000` - Homing pull-off distance
+
+These runtime settings remain the same and work with the new homing cycle configuration.
+
+## Performance Impact
+
+**Homing Time:** Sequential homing takes slightly longer than simultaneous (~few seconds), but provides 100% reliability.
+
+**Safety:** Better control over axis movement sequence.