[Easy] Fix numbering typo in Llama README docs (pytorch#9936)

### Summary
Numbering scheme jumps from 4-> 6


![image](https://github.com/user-attachments/assets/3d1876f2-b72f-400d-85bf-16679c21077b)

![image](https://github.com/user-attachments/assets/8fca230b-c989-484d-9411-40418c55721d)


### Test plan
Markdown


cc @mergennachin @byjlw

Author: Jack-Khuu

examples/models/llama/README.md

@@ -371,7 +371,7 @@ adb push cmake-out-android/examples/models/llama/llama_main /data/local/tmp/llam
 ```
 adb shell "cd /data/local/tmp/llama && ./llama_main --model_path <model.pte> --tokenizer_path <tokenizer.model> --prompt \"What is the capital of France?\" --seq_len 120" --warmup=1
 ```
-## Step 6: Build Mobile apps
+## Step 5: Build Mobile apps
 
 ### iOS