Add Ubuntu 20.04, CentOS 8 and Amazon Linux 2 package bots to README

Author: shahmishal

README.md

@@ -8,6 +8,9 @@
 | **macOS**        | x86_64 |[![Build Status](https://ci.swift.org/job/oss-swift-incremental-RA-osx/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-incremental-RA-osx)|[![Build Status](https://ci.swift.org/job/oss-swift-package-osx/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-osx)|
 | **Ubuntu 16.04** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-16_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-16_04)|[![Build Status](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-16_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-16_04)|
 | **Ubuntu 18.04** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-18_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-incremental-RA-linux-ubuntu-18_04)|[![Build Status](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-18_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-18_04)|
+| **Ubuntu 20.04** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-package-ubuntu-20_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-ubuntu-20_04)|[![Build Status](https://ci.swift.org/job/oss-swift-package-ubuntu-20_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-ubuntu-20_04)|
+| **CentOS 8** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-package-centos-8/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-centos-8)|[![Build Status](https://ci.swift.org/job/oss-swift-package-linux-ubuntu-18_04/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-centos-8)|
+| **Amazon Linux 2** | x86_64 | [![Build Status](https://ci.swift.org/job/oss-swift-package-amazon-linux-2/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-amazon-linux-2)|[![Build Status](https://ci.swift.org/job/oss-swift-package-amazon-linux-2/lastCompletedBuild/badge/icon)](https://ci.swift.org/job/oss-swift-package-amazon-linux-2)|
 
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