docs: update README

Author: codinaut

README.md

@@ -1,3 +1,12 @@
 # envtestkit
 
-**_Under development._**
+Test kit for logics with environment variable involvements.
+
+[![ci](https://github.com/codinaut/envtestkit/workflows/ci/badge.svg)](https://github.com/codinaut/envtestkit/actions?query=workflow%3Aci)
+[![crates.io](https://img.shields.io/crates/v/envtestkit.svg)](https://crates.io/crates/envtestkit)
+[![docs.rs](https://docs.rs/envtestkit/badge.svg)](https://docs.rs/crate/envtestkit)
+[![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg)](https://github.com/semantic-release/semantic-release)
+
+## License
+
+[MIT](LICENSE).