bump version to 4.8.0 (#190)

* bump version to 4.8.0

* update benchmark results on i7 & rpi

* correct python command on i7

* update results on jetson nano

* update results on atlas 200 cpu

* update results on vim3 cpu, sunrise x3 cpu

* update results on vim3 npu

* update results on edge2

* update results on rv1126 and vision2

* update results on axp

* update table

README.md

@@ -22,7 +22,7 @@ python demo.py --input /path/to/image -v
 ```
 Note: 
 - image result saved as "result.jpg"
-- this model requires `opencv-python>=4.7.0`
+- this model requires `opencv-python>=4.8.0`
 
 
 ## Results

demo.py

@@ -5,7 +5,7 @@ import argparse
 from yolox import YoloX
 
 # Check OpenCV version
-assert cv.__version__ >= "4.7.0", \
+assert cv.__version__ >= "4.8.0", \
        "Please install latest opencv-python to try this demo: python3 -m pip install --upgrade opencv-python"
 
 # Valid combinations of backends and targets