Readme for frontend configuration doesn't show default values

[paskal]

Setup on your website "Comments" section shows frontend configuration with non-default values and defaults ones written in the comments: I propose to have all default values listed there and mark if a key is optional and what values it can take other than the default in the comments.

For example

// currently
show_email_subscription: false // optional param; by default it is `true` <...>
// should be
show_email_subscription: true // optional param