Specify the user behaviors namespace

Adding only `:lt.objs.langs.ruby/use-rbenv` to user behaviors produces the error `Invalid settings file: user.behaviors Error: Map literal must contain an even number of forms`.

Since people who use the plugin might not know Clojure (like myself), maybe it's better to specify the whole configuration code that should be written, in order to avoid confusions (I had to look at ruby.behaviors in order to understand how to use those configurations).