docs: Add P0300 code and spark plugs pending items from Diagnosis project

- Added P0300 diagnostic code reference to FuelPressureIssue/progress.md
- Added spark plugs pending maintenance to FuelPressureIssue/progress.md
- Added both items to main README.md Notes section for visibility
- Ensures all information from 2002-Chevy-Express-Diagnosis project is preserved

FuelPressureIssue/progress.md

@@ -170,3 +170,20 @@
 - **Parts sourcing:** Use local auto parts store with VIN lookup for correct pump and filter
 - **Old fuel filter:** Remove old filter first to confirm it's the correct part before buying new one
 - **Quality concern:** Bought cheapest option (~$8 vs ~$15-20 for premium brands); monitor for leaks or premature failure
+
+---
+
+## 🔧 Related Diagnostics & Pending Items
+
+### Diagnostic Codes
+- **P0300** - Random/Multiple Cylinder Misfire Detected
+  - **Context:** Code was present during crank no-start diagnosis (resolved with distributor repair)
+  - **Status:** Should be cleared after fuel system repair
+  - **Location:** Diagnosed in 2002-Chevy-Express-Diagnosis project (2026-03-20)
+
+### Pending Maintenance
+- **Spark Plugs** - Replace all 8 (matching set)
+  - **Urgency:** Low - can wait, not affecting current operation
+  - **Estimated cost:** ~$30-50
+  - **Status:** Awaiting fuel system repair first, then will replace plugs
+  - **Location:** Documented in 2002-Chevy-Express-Diagnosis project (2026-03-21)