[skip ci] Update README.md. (#697)

1. Change "API" to "SDK".
2. Fix the "all contributors" badge.

README.md

 
-<!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->[![All Contributors](https://img.shields.io/badge/all_contributors-1-orange.svg?style=flat-square)](#contributors-)<!-- ALL-CONTRIBUTORS-BADGE:END -->
 ![Milvuslogo](https://github.com/milvus-io/docs/blob/master/assets/milvus_logo.png)
 
 [![Slack](https://img.shields.io/badge/Join-Slack-orange)](https://join.slack.com/t/milvusio/shared_invite/enQtNzY1OTQ0NDI3NjMzLWNmYmM1NmNjOTQ5MGI5NDhhYmRhMGU5M2NhNzhhMDMzY2MzNDdlYjM5ODQ5MmE3ODFlYzU3YjJkNmVlNDQ2ZTk)
@@ -9,9 +8,7 @@
 ![Release](https://img.shields.io/badge/release-v0.6.0-yellowgreen)
 ![Release_date](https://img.shields.io/badge/release%20date-December-yellowgreen)
 [![codecov](https://codecov.io/gh/milvus-io/milvus/branch/master/graph/badge.svg)](https://codecov.io/gh/milvus-io/milvus)
-<!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
-[![All Contributors](https://img.shields.io/badge/all_contributors-1-orange.svg?style=flat-square)](#contributors-)
-<!-- ALL-CONTRIBUTORS-BADGE:END -->
+[![All Contributors](https://img.shields.io/badge/all_contributors-3-orange.svg?style=flat-square)](#contributors-)
 
 [中文版](README_CN.md) | [日本語版](README_JP.md)
 
@@ -21,9 +18,9 @@ Milvus is the world's fastest similarity search engine for massive-scale feature
 
 For more detailed introduction of Milvus and its architecture, see [Milvus overview](https://www.milvus.io/docs/en/aboutmilvus/overview/).
 
-Milvus provides stable [Python](https://github.com/milvus-io/pymilvus), [Java](https://github.com/milvus-io/milvus-sdk-java) and [C++](https://github.com/milvus-io/milvus/tree/master/core/src/sdk) APIs. 
+Milvus provides stable [Python](https://github.com/milvus-io/pymilvus), [Java](https://github.com/milvus-io/milvus-sdk-java) and [C++](https://github.com/milvus-io/milvus/tree/master/core/src/sdk) SDKs. 
 
-Keep up-to-date with newest releases and latest updates by reading Milvus [release notes](https://www.milvus.io/docs/en/release/v0.5.3/).
+Keep up-to-date with newest releases and latest updates by reading Milvus [release notes](https://www.milvus.io/docs/en/release/v0.6.0/).
 
 ## Get started
 
@@ -75,9 +72,6 @@ Below is a list of Milvus contributors. We greatly appreciate your contributions
 <!-- prettier-ignore-end -->
 <!-- ALL-CONTRIBUTORS-LIST:END -->
 
-- [akihoni](https://github.com/akihoni) provided the CN version of README, and found a broken link in the doc.
-- [goodhamgupta](https://github.com/goodhamgupta) fixed a filename typo in the bootcamp doc.
-- [erdustiggen](https://github.com/erdustiggen) changed from std::cout to LOG for error messages, and fixed a clang format issue as well as some grammatical errors.
 
 ## Resources