Add badge

Author: wata727

README.md

@@ -1,4 +1,5 @@
 # TFLint plugin SDK
+[![Build Status](https://github.com/terraform-linters/tflint-plugin-sdk/workflows/build/badge.svg?branch=master)](https://github.com/terraform-linters/tflint-plugin-sdk/actions)
 [![GitHub release](https://img.shields.io/github/release/terraform-linters/tflint-plugin-sdk.svg)](https://github.com/terraform-linters/tflint-plugin-sdk/releases/latest)
 [![License: MPL 2.0](https://img.shields.io/badge/License-MPL%202.0-blue.svg)](LICENSE)
 
@@ -9,7 +10,7 @@ NOTE: This plugin system is experimental. This means that API compatibility is f
 ## Requirements
 
 - TFLint v0.14+
-- Go v1.13
+- Go v1.14
 
 ## Usage