[doc]: Update README.md (#70)

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Author: qiluo-msft

README.md

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+[![Total alerts](https://img.shields.io/lgtm/alerts/g/Azure/sonic-py-swsssdk.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/Azure/sonic-py-swsssdk/alerts/)
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 # Python SwSS SDK
 Python utility library for SONiC Switch State Service database access