Update README

README.md

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-# MLIR Hello Dialect
+# MLIR Hello Dialect ![nightly build status](https://github.com/Lewuathe/mlir-hello/actions/workflows/nightly-build.yml/badge.svg)
 
 This is the minimal example to look into the way to implement the hello-world kind of program with MLIR. The basic code structure is borrowed from [standalone](https://github.com/llvm/llvm-project/tree/main/mlir/examples/standalone) and [Toy language](https://github.com/llvm/llvm-project/tree/main/mlir/examples/toy) in LLVM project.
 
+We constantly check the compatibility with the latest LLVM/MLIR in [the nightly build](https://github.com/Lewuathe/mlir-hello/actions/workflows/nightly-build.yml). The status of the build is shown in the badge above.
+
 ## Prerequisites
 
 * [LLVM](https://llvm.org/)