docs: add Ampli SDK reference (#507)

Author: qingzhuozhen

README.md

@@ -16,6 +16,9 @@
 # Official Amplitude JS/Web SDK
 A JavaScript SDK for tracking events and revenue to [Amplitude](https://www.amplitude.com).
 
+## Amplitude and Ampli SDK
+[Ampli SDK](https://developers.data.amplitude.com/ampli-sdk-overview/) is autogenerated library based on your pre-defined [tracking plan](https://developers.data.amplitude.com/what-is-a-tracking-plan). The Ampli SDK, is a lightweight wrapper over the Amplitude SDK that provides type-safety, supports linting, and enables features like input validation. The code replicates the spec in the Tracking Plan and enforces its rules and requirements. This repository is about **Amplitude SDK**. To learn more about Ampli SDK, please refer to the [Ampli Browser](https://developers.data.amplitude.com/browser-ampli) and [examples](https://github.com/amplitude/ampli-examples).
+
 ## Installation and Quick Start
 * For using the SDK, please visit our :100:[Developer Center](https://developers.amplitude.com/docs/javascript).
 * For developing the SDK, please visit our [CONTRIBUTING.md](https://github.com/amplitude/Amplitude-JavaScript/blob/main/CONTRIBUTING.md).