Add codacy code quality badge to the README.md

Author: Anand Sanmukhani

README.md

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 # prometheus-connect
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+[![Codacy Badge](https://api.codacy.com/project/badge/Grade/48cebb81b5d34d7cb45bcc5f5e0d505b)](https://app.codacy.com/app/4n4nd/prometheus-connect?utm_source=github.com&utm_medium=referral&utm_content=4n4nd/prometheus-connect&utm_campaign=Badge_Grade_Settings)
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 A python wrapper for the prometheus http api