In /user/plugins, create a new folder named BlackListIP
In this new directory, copy the plugin.php file from this repository
Go to the Plugins administration page and activate the plugin
Currently, the IP addresses to blacklist have to be entered in the config.php (should be into the /user directory)with following format :
$yourls_blacklist_ip = array ("149.3.136.114","119.180.110.179"); with one IP per quotes.
I'm currently working on an admin page to enter those IPs.
Roadmap contains the possibility to use regexp to specify the IP addresses. No, no date provided :)