Merge pull request #5532 from taosdata/docs/sangshuduo/TD-3430-cmake-minimal-version-is-2.8.12.x

[TD-3430] <docs>: cmake minimal version is 2.8.12.x.

README.md

@@ -31,7 +31,7 @@ For user manual, system design and architecture, engineering blogs, refer to [TD
 # Building
 At the moment, TDengine only supports building and running on Linux systems. You can choose to [install from packages](https://www.taosdata.com/en/getting-started/#Install-from-Package) or from the source code. This quick guide is for installation from the source only.
 
-To build TDengine, use [CMake](https://cmake.org/) 3.5 or higher versions in the project directory. 
+To build TDengine, use [CMake](https://cmake.org/) 2.8.12.x or higher versions in the project directory. 
 
 ## Install tools