Support site_root_url placeholder in "default" preview client url

[jaap3]

Fixes #16

I got stuck on updating the docs. Hope it's clear enough/acceptable

[jaap3]

The heck? The linting issue is on a line I didn't touch at all

[jaap3]

@zerolab are you interested in this?

[zerolab]

@jaap3 yes. it slipped under my radar. Will try to review this in the coming days!

[jaap3]

🔔 hope you get some time to review this before the one year anniversary ;-)

[zerolab]

@jaap3 adding to the list of things to check next week. Will give this package some much needed love and attention

[zerolab]

Hey @jaap3 merged in d184f7d and parents

I made a tweak in 91e8af4 that changed the placeholder to {SITE_ROOT_URL}

Will look at making a new release this afternoon

[jaap3]

Thank you!