When a developer is creating a library, or any other software package, that they want others to use it is absolutely vital that they choose a license for the project that will allow their target audience to use it.
It is just as important that the licensing information is included among the files that are downloaded when someone gets a copy of the library.
Most people remember these steps, but they are occasionally forgotten.
What is JUST AS IMPORTANT however, is to find some way to inform people who are downloading your code from a website or some other source of what the license is before they download it.
If I don’t know the licensing terms of your code, I am most likely just not going to download it. If I am working on a project, and I am looking for a library to make it easier, then I am looking for libraries that are released under compatible licenses. If the license is incompatible, then the code isn’t worth much to me at the time. It is a waist of my time and your bandwidth for me to download a library I can’t use.
This is especially sad when the developer has taken the time to create a beautiful website with a lot of description of what the program is, and does, but then they forget one of the most important pieces of information.
Please, if your code is licensed as GPL, say so on the site. If your code is BSD licensed, say so someplace on the site. Whatever license you use, display it proudly. If you are using a git repo, and it is set up to be web viewable, this is perfect. You can include it in the README file that your git repo software most likely wants to display to the web anyway.
If you are just offering tarballs/zips. then just include it on the download page.
To be honest, there are two common practices that I have seen most often on websites for successful projects. That is to either include the licensing information on the About page, or to just have a page that specifically addresses licensing issues. In either case, these would be included in the navigation bar/pain/whatever on the website.
Once you have already done all the work of making the code worthy of public display, you owe it to the project to take the last few steps needed to encourage adoption.