Update README.md 📝

Added very basic readme file. Added build status and NuGet package version badges.

README.md

@@ -1 +1,26 @@
-# notion-sdk-net
+<div align="center>
+    <h1>Notion SDK for .Net</h1>
+    <p>
+        <b>A simple and easy to use client for the <a href="https://developers.notion.com">Notion API</a></b>
+    </p>
+</div>
+
+![Build Status](https://github.com/notion-dotnet/notion-sdk-net/actions/workflows/ci_build.yml/badge.svg)
+
+![Nuget](https://img.shields.io/nuget/v/Notion.Net)
+![Nuget (with prereleases)](https://img.shields.io/nuget/vpre/Notion.Net)
+
+## Installation
+
+.Net CLI
+```
+dotnet add package Notion.Net
+```
+
+## Usage
+
+Todo
+
+## Contribution Guideline
+
+At the moment I haven't got any specific guidelines for the project. Everyone are welcome to contribute.