batch-clone: git clone remote repositories in batch

Run script without argv, default is homework.txt

Each repository should be single line in homework.txt

python batch-clone.py

Run script with argv xxxx.txt

python batch-clone.py chengdu.txt
python batch-clone.py beijing.txt
python batch-clone.py xian.txt
python batch-clone.py wuhan.txt

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All repositories will be cloned into the same file name directory