docs: add hex, docs, and CI badges to README

Author: fahchen

README.md

@@ -1,5 +1,8 @@
 # EctoTypedSchema
 
+[![Hex.pm](https://img.shields.io/hexpm/v/ecto_typed_schema.svg)](https://hex.pm/packages/ecto_typed_schema)
+[![Hex Docs](https://img.shields.io/badge/hex-docs-blue.svg)](https://hexdocs.pm/ecto_typed_schema)
+[![CI](https://github.com/fahchen/ecto_typed_schema/actions/workflows/elixir.yml/badge.svg)](https://github.com/fahchen/ecto_typed_schema/actions/workflows/elixir.yml)
 [![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](LICENSE)
 
 Ecto schemas don't generate `@type t()` specs. You either maintain them by hand