Update pytorch-ssd.md

[MohammadRobot]

update the following arguments:-
--epochs ==> --num-epochs
--workers ==> --num-workers

[dusty-nv]

Hi @MohammadRobot , the train_ssd.py script had previously been updated to accept --epochs and --workers. This is so it is consistent with the classification/train.py script and classification documentation.

[MohammadRobot]

Hi @dusty-nv, I got this error "train_ssd.py: error: unrecognized arguments: --epochs=30" when I run the following script:
$ python3 train_ssd.py --data=data/fruit --model-dir=models/fruit --batch-size=4 --epochs=30

The following script run without any issue:
$ python3 train_ssd.py --data=data/fruit --model-dir=models/fruit --batch-size=4 --num-epochs=30