[TD-6420]<docs>: update README.md for apt-get install. (#8106)

* [TD-6420]<docs>: update README.md for apt-get install.

* add section to getting-started part.

README.md

@@ -202,6 +202,19 @@ taos
 
 If TDengine shell connects the server successfully, welcome messages and version info are printed. Otherwise, an error message is shown.
 
+## Install TDengine by apt-get
+
+If you use Debian or Ubuntu system, you can use 'apt-get' command to intall TDengine from official repository. Please use following commands to setup:
+
+```
+wget -qO - http://repos.taosdata.com/tdengine.key | sudo apt-key add -
+echo "deb [arch=amd64] http://repos.taosdata.com/tdengine-stable stable main" | sudo tee /etc/apt/sources.list.d/tdengine-stable.list
+[Optional] echo "deb [arch=amd64] http://repos.taosdata.com/tdengine-beta beta main" | sudo tee /etc/apt/sources.list.d/tdengine-beta.list
+sudo apt-get update
+apt-get policy tdengine
+sudo apt-get install tdengine
+```
+
 ## Quick Run
 
 If you don't want to run TDengine as a service, you can run it in current shell. For example, to quickly start a TDengine server after building, run the command below in terminal: (We take Linux as an example, command on Windows will be `taosd.exe`)

documentation20/cn/02.getting-started/docs.md

@@ -22,6 +22,18 @@ TDengine 的安装非常简单，从下载到安装成功仅仅只要几秒钟
 
 具体的安装过程，请参见 [TDengine 多种安装包的安装和卸载](https://www.taosdata.com/blog/2019/08/09/566.html) 以及 [视频教程](https://www.taosdata.com/blog/2020/11/11/1941.html)。
 
+### 使用 apt-get 安装
+
+如果使用 Debian 或 Ubuntu 系统，也可以使用 apt-get 从官方仓库安装，设置方法为：
+```
+wget -qO - http://repos.taosdata.com/tdengine.key | sudo apt-key add -
+echo "deb [arch=amd64] http://repos.taosdata.com/tdengine-stable stable main" | sudo tee /etc/apt/sources.list.d/tdengine-stable.list
+[ beta 版安装包仓库为可选安装项 ] echo "deb [arch=amd64] http://repos.taosdata.com/tdengine-beta beta main" | sudo tee /etc/apt/sources.list.d/tdengine-beta.list
+sudo apt-get update
+apt-get policy tdengine
+sudo apt-get install tdengine
+```
+
 <a class="anchor" id="start"></a>
 ## 轻松启动
 

documentation20/en/02.getting-started/docs.md

@@ -20,6 +20,19 @@ Three different packages for TDengine server are provided, please pick up the on
 
 Click [here](https://www.taosdata.com/en/getting-started/#Install-from-Package) to download the install package.
 
+### Install TDengine by apt-get
+
+If you use Debian or Ubuntu system you can use 'apt-get' command to install TDengine from official repository. Please use following commands to setup:
+
+```
+wget -qO - http://repos.taosdata.com/tdengine.key | sudo apt-key add -
+echo "deb [arch=amd64] http://repos.taosdata.com/tdengine-stable stable main" | sudo tee /etc/apt/sources.list.d/tdengine-stable.list
+[Optional] echo "deb [arch=amd64] http://repos.taosdata.com/tdengine-beta beta main" | sudo tee /etc/apt/sources.list.d/tdengine-beta.list
+sudo apt-get update
+apt-get policy tdengine
+sudo apt-get install tdengine
+```
+
 ## <a class="anchor" id="start"></a>Quick Launch
 
 After installation, you can start the TDengine service by the `systemctl` command.
@@ -218,4 +231,4 @@ Comparison matrix as following:
 
 Note: ● has been verified by official tests; ○ has been verified by unofficial tests.
 
-Please visit Connectors section for more detailed information.
+Please visit Connectors section for more detailed information.
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