Update greetings.yml (#6165)

.github/workflows/greetings.yml

 
             [**Python>=3.6.0**](https://www.python.org/) with all [requirements.txt](https://github.com/ultralytics/yolov5/blob/master/requirements.txt) installed including [**PyTorch>=1.7**](https://pytorch.org/get-started/locally/). To get started:
             ```bash
-            $ git clone https://github.com/ultralytics/yolov5
-            $ cd yolov5
-            $ pip install -r requirements.txt
+            git clone https://github.com/ultralytics/yolov5  # clone
+            cd yolov5
+            pip install -r requirements.txt  # install
             ```
 
             ## Environments