The TL, DR version of sharing with No License, is that technically speaking you are not explicitly permitting others to use your code in any way, just allowing them to look, a license is a formal way to give permissions to others to copy, modify, or use your code.
You don’t need an extra file for the license, you can embed it on a section at the top of your file, as you did with the description, just add a # License section at the very top, if you want the most permissive one you can just use MIT, just need to replace the year of publication of the code, and you can use a pseudonym/username like ‘hereforawhile@lemmy.ml’ if you don’t want to use something like email, username on another site or real name, that can be used to identify you, if that’s a concern
A friendly reminder that it is best to wait a bit before updating, in case there are any bugs still there, happened a few days ago with Forgejo, that a mayor bug was detected after initial release of v13.0