Write README.md

Author: tsub

README.md

@@ -1,2 +1,18 @@
 # docker-mruby-cli
-Docker image for mruby-cli :whale:
+
+Docker image for [mruby-cli] :whale:
+
+## Usage
+
+```
+$ docker pull tsub/mruby-cli
+
+# Generate a new mruby CLI
+$ docker run -it -v $PWD:$PWD -w $PWD tsub/mruby-cli --setup my-cli
+```
+
+## Get more details
+
+See [mruby-cli]
+
+[mruby-cli]: https://github.com/hone/mruby-cli