fix readme formatting

README.md

@@ -8,11 +8,14 @@ Usage
 Build the container with `docker build -t 'tag name' .`. Install the `mean` and `start-mongodb` to `~/bin` or some other location in the path.
 
 To run commands from the container, use `mean <command>`. For example, to install a new npm package globally:
+
     mean npm install -g generator-polymer
 
 Or to create a yeoman scaffolding in the current folder:
+
     mean yo polymer
 
 Some default npm and gem packages are specified in `default-packages.sh`. They can be installed with:
+
     mean bash default-packages.sh