* Update default `--epochs 100`

@AyushExel @kalenmike updating default Detection and Segmentation trainings to 100 epochs
Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Update train.py
Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Update README.md
Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Update README_cn.md
Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>