README.md: update build status badges

This commit:

- Replaces the broken GitLab CI badge link (reference: https://docs.gitlab.com/ee/ci/pipelines/settings.html#pipeline-status-badge).
- Adds the Azure Pipelines badge for the Nightly pipeline.
- Adds the Cirrus CI badge.
- Rearranges the badges in a table.

README.md

@@ -1,6 +1,13 @@
 # SoftEther VPN
 
-[![AppVeyor build status](https://ci.appveyor.com/api/projects/status/github/softethervpn/softethervpn?branch=master&svg=true)](https://ci.appveyor.com/project/softethervpn/softethervpn) [![Travis CI build status](https://travis-ci.org/SoftEtherVPN/SoftEtherVPN.svg?branch=master)](https://travis-ci.org/SoftEtherVPN/SoftEtherVPN) [![gitlab-ci build status](https://gitlab.com/SoftEther/SoftEtherVPN/badges/master/build.svg)](https://gitlab.com/SoftEther/SoftEtherVPN/pipelines) [![Coverity Scan Build Status](https://scan.coverity.com/projects/16304/badge.svg)](https://scan.coverity.com/projects/softethervpn-softethervpn)
+||Badges|
+|---|---|
+|AppVeyor|[![AppVeyor build status](https://ci.appveyor.com/api/projects/status/github/softethervpn/softethervpn?branch=master&svg=true)](https://ci.appveyor.com/project/softethervpn/softethervpn) |
+|Travis CI|[![Travis CI build status](https://travis-ci.org/SoftEtherVPN/SoftEtherVPN.svg?branch=master)](https://travis-ci.org/SoftEtherVPN/SoftEtherVPN) |
+|GitLab CI|[![GitLab CI build status](https://gitlab.com/SoftEther/SoftEtherVPN/badges/master/pipeline.svg)](https://gitlab.com/SoftEther/SoftEtherVPN/pipelines)|
+|Coverity Scan|[![Coverity Scan build status](https://scan.coverity.com/projects/16304/badge.svg)](https://scan.coverity.com/projects/softethervpn-softethervpn)|
+|Azure Pipelines|[![Azure Pipelines build status for Nightly](https://dev.azure.com/SoftEther-VPN/SoftEther%20VPN/_apis/build/status/6?api-version=6.0-preview.1)](https://dev.azure.com/SoftEther-VPN/SoftEther%20VPN/_build?definitionId=6)|
+|Cirrus CI|[![Cirrus CI build status](https://api.cirrus-ci.com/github/SoftEtherVPN/SoftEtherVPN.svg)](https://cirrus-ci.com/github/SoftEtherVPN/SoftEtherVPN)|
 
 - [SoftEther VPN](#softether-vpn)
 - [BOARD MEMBERS OF THIS REPOSITORY](#board-members-of-this-repository)