CC BY 4.0
Here explained briefly, but please read the full license description here

• i. You may reproduce and redistribute the content in any format or medium for any purpose, as well as remix, modify and build on the content, even for commercial purposes.
• ii. You must provide proper copyright and legal information, attach a link to the license, and indicate if changes have been made. This information may be provided in any reasonable manner, but not in a way that gives the impression that the licensor is specifically supporting you or your use.