add badges

Author: gkorland

README.md

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+[![license](https://img.shields.io/github/license/RediSearch/redisearch-api-rs.svg)](https://github.com/RediSearch/redisearch-api-rs)
+[![GitHub issues](https://img.shields.io/github/release/RediSearch/redisearch-api-rs.svg)](https://github.com/RediSearch/redisearch-api-rs/releases/latest)
+[![CircleCI](https://circleci.com/gh/RediSearch/redisearch-api-rs/tree/master.svg?style=svg)](https://circleci.com/gh/RediSearch/redisearch-api-rs/tree/master)
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 # redisearch-api-rs
 
 ## Rust API for RediSearch