Confirm on script install you can change the mastodon urls

[tomouchuu]

At the moment the script will only run on the instance I'm a part of (niu.moe).

It would be nice rather than me having to add all the instances which'll be a constant hard battle, to on install, a user could say what instance they're on so the script will hook onto that.

[tomouchuu]

With that commit we now target all mastodon instances but could also now run on any webpage that matches the new @ match rule. So not closing for the moment, til a better solution happens

Edit: apologies to tagging @ match

[tomouchuu]

So in addition to the not amazing match rule which has been further supplemented with *://*/settings/preferences for the preferences page. When saving preferences it takes you to the root of the domain (ie. niu.moe) which doesn't match either rules, so this is why you then need to refresh on the feed page to reactivate the script.