docs: improve the documentation of alpine (#134)
diff --git a/alpine/README.MD b/alpine/README.MD
index e9f00e9..a977a64 100644
--- a/alpine/README.MD
+++ b/alpine/README.MD
@@ -1,5 +1,7 @@
### When building with `alpine` basic image, please specify `APISIX_VERSION` through `build-arg`
+```shell
+$ docker build --build-arg APISIX_VERSION=$APISIX_VERSION -t $IMAGE_NAME .
```
-docker build --build-arg APISIX_VERSION=$APISIX_VERSION -t $IMAGE_NAME .
-```
\ No newline at end of file
+
+Note: The minimum version of docker that supports building image is `docker 17.05.0-ce`.
