Update README.md (ultralytics#2934)

* Update README.md

dependencies:
ImportError: libGL.so.1: cannot open shared object file: No such file or directory
ImportError: libgthread-2.0.so.0: cannot open shared object file: No such file or directory
ImportError: libSM.so.6: cannot open shared object file: No such file or directory
ImportError: libXrender.so.1: cannot open shared object file: No such file or directory

* replace older apt-get with apt

Code commented for now until a better understanding of the issue, and also code is not cross-platform compatible.

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

README.md

@@ -58,6 +58,7 @@ Model |size<br><sup>(pixels) |mAP<sup>val<br>0.5:0.95 |mAP<sup>test<br>0.5:0.95
 ## Requirements
 
 Python 3.8 or later with all [requirements.txt](https://github.com/ultralytics/yolov5/blob/master/requirements.txt) dependencies installed, including `torch>=1.7`. To install run:
+<!-- $ sudo apt update && apt install -y libgl1-mesa-glx libsm6 libxext6 libxrender-dev -->
 ```bash
 $ pip install -r requirements.txt
 ```