(doc) Fix passing of debug argument

Also changed the formatting slightly.

docker/README.md

@@ -8,9 +8,9 @@ To build this image yourself, follow these steps:
 1. Clone down the repository using `git clone https://github.com/chocolatey/choco.git`.
 1. Change directories to the root of the repository.
 1. Run the docker build command. `docker build -t mono-choco -f docker/Dockerfile.linux .` (the trailing . is important)
-    To build a official version, add the argument `--build-arg buildscript=build.official.sh`
-    To build a debug version, add the argument `--build-arg buildscript=build.official.sh`
-    To change the version of mono used, add the argument `--build-arg monoversion=mono-tag`
+    * To build a official version, add the argument `--build-arg buildscript=build.official.sh`
+    * To build a debug version, add the argument `--build-arg buildscript=build.debug.sh`
+    * To change the version of mono used, add the argument `--build-arg monoversion=mono-tag`
 1. Run your new image using the command `docker run -ti --rm mono-choco /bin/bash`
 1. Test choco by running `choco -h`. You should see the help message from choco.exe.