diff --git a/docker/README.md b/docker/README.md
index 574d4ac..ca4e368 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -1,5 +1,12 @@
 This docker image wraps [shellcheck](https://github.com/koalaman/shellcheck) as a single executable.
 
-How to use it? For example, you have a shell script named `sample.sh` under the current directory, you can lint it by running:
+## Build the image
+
+    cd shellcheck/docker
+    docker build -t shellcheck .
+
+## How to use it
+
+For example, you have a shell script named `sample.sh` under the current directory, you can lint it by running:
 
     docker run -v $(pwd):/tmp/work shellcheck /tmp/work/sample.sh