Use the library however you want, but display the message “This creation includes software developed by Echo Hollow.” somewhere that the player gets to see it at least once. While not required, I'd sure appreciate a linkback, too.

In Sugarcube 2, you might cut-and-paste the following into your intro blurb or place it at the bottom of your sidebar in small text:

This creation includes software developed by <a target="_blank" href="http://www.echohollow.net">Echo Hollow</a>.

Copyright (c) 2023 Echo Hollow. All rights reserved.

Redistribution and use in source and binary forms, with or without 
 modification, are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright 
       notice, this list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright 
       notice, this list of conditions and the following disclaimer in the 
       documentation and/or other materials provided with the distribution.
    3. All advertising materials mentioning features or use of this software 
       must display the following acknowledgement:
         "This creation includes software developed by Echo Hollow."
    4. Neither the name of the copyright holder nor the names of its 
       contributors may be used to endorse or promote products derived from 
       this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY COPYRIGHT HOLDER "AS IS" AND ANY EXPRESS OR 
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO 
EVENT SHALL COPYRIGHT HOLDER BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 
OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 
OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.