Add usage and examples for crawl.py
Add usage and examples for crawl.py

memex-explorer/nutch-python,sujen1412/nutch-python,YongchaoShang/nutch-python,sujen1412/nutch-python,chrismattmann/nutch-python,memex-explorer/nutch-python,chrismattmann/nutch-python,YongchaoShang/nutch-python