docs: update readme.

README.md

@@ -1,2 +1,51 @@
 # collection
-Generic collections framework for Golang.
+
+![Test](https://github.com/ghosind/collection/workflows/collection/badge.svg)
+[![codecov](https://codecov.io/gh/ghosind/collection/branch/main/graph/badge.svg)](https://codecov.io/gh/ghosind/collection)
+[![Latest version](https://img.shields.io/github/v/release/ghosind/collection?include_prereleases)](https://github.com/ghosind/collection)
+![License Badge](https://img.shields.io/github/license/ghosind/collection)
+[![Go Reference](https://pkg.go.dev/badge/github.com/ghosind/collection.svg)](https://pkg.go.dev/github.com/ghosind/collection)
+
+Generics collections framework for Golang.
+
+> IMPORTANT NOTICE: This package requires Go version 1.18+.
+
+## Overview
+
+This package provides the following data structure interfaces and implementations:
+
+- `Collection`: The root interface of most of the structures in this package.
+
+- `Set`: A collection interface that contains no duplicate elements.
+
+    - [`HashSet`](https://pkg.go.dev/github.com/ghosind/collection#HashSet): The implementation of Set based on Go built-in map structure.
+
+## Installation
+
+You can install this package by the following command.
+
+```sh
+go get -u github.com/ghosind/collection
+```
+
+After installation, you can import it by the following code.
+
+```go
+import "github.com/ghosind/collection"
+```
+
+## Examples
+
+### HashSet Examples
+
+Create a string set, add and test elements in the set.
+
+```go
+fruits := collection.NewHashSet[string]()
+
+fruits.Add("Apple")
+fruits.Add("Banana")
+
+log.Print(fruits.Contains("Banana")) // true
+log.Print(fruits.Contains("Lemon"))
+```