Update the installation guide

The new order of the commands will ensure that the user will see the
generated app using the latest stylesheets (without having to save any
files initially) and the watch command will be running after opening
the app in the browser, so that all changes will be updated.
Replace incorrect <navi> element to <nav>

So that the app is using the valid HTML5 <nav> tag
Merge pull request #1 from heartcode/master

Minor updates