docs(readme): documentation reference.

- Add Codecov and Go Report Card badges to README.md
- Add cover.png image to images folder
- Add an OpenAI Chat completions documentation reference

Author: appleboy

README.md

@@ -1,5 +1,15 @@
 # CodeGPT
 
 [![Lint and Testing](https://github.com/appleboy/CodeGPT/actions/workflows/testing.yml/badge.svg?branch=main)](https://github.com/appleboy/CodeGPT/actions/workflows/testing.yml)
+[![codecov](https://codecov.io/gh/appleboy/CodeGPT/branch/main/graph/badge.svg)](https://codecov.io/gh/appleboy/CodeGPT)
+[![Go Report Card](https://goreportcard.com/badge/github.com/appleboy/CodeGPT)](https://goreportcard.com/report/github.com/appleboy/CodeGPT)
 
-A [git prepare-commit-msg hook](https://git-scm.com/docs/githooks) using ChatGPT written in [Golang](https://go.dev).
+![cover](./images/cover.png)
+
+A CLI written in [Golang](https://go.dev) that writes your git commit messages for you with ChatGPT AI (`gpt-3.5-turbo` model) and install a [git prepare-commit-msg hook](https://git-scm.com/docs/githooks) automatically.
+
+## Installation
+
+## Reference
+
+* [OpenAI Chat completions documentation](https://platform.openai.com/docs/guides/chat).