Document specify doctor command in README

Author: KhawarHabibKhan

README.md

@@ -67,6 +67,9 @@ specify init --here --ai claude
 
 # Check installed tools
 specify check
+
+# Diagnose project health
+specify doctor
 ```
 
 To upgrade Specify, see the [Upgrade Guide](./docs/upgrade.md) for detailed instructions. Quick upgrade:
@@ -283,6 +286,9 @@ specify init --here --ai gemini --ai-skills
 
 # Check system requirements
 specify check
+
+# Diagnose project health
+specify doctor
 ```
 
 ### Available Slash Commands