How should one distribute the Javadoc for a Library?

I'd include the library .jar and the documentation and other things, like a README, License file etc. in a single archive (zip or tar.gz)

mylib-1.0.1.tar.gz , which contains:

mylib-1.0.1/
           ├── javadoc
           │   └── index.html  (and all other javadoc files under here)
           ├── mylib-1.0.1.jar
           └── README

Instead of the expanded javadoc/ sub directory within the archive, you could add the compressed javadoc in a mylib-1.0.1-javadoc.jar (or zip) , both options are common.

mylib-1.0.1/
           ├── mylib-1.0.1-javadoc.jar
           ├── mylib-1.0.1.jar
           └── README

It's a general practice to keep the JavaDocs in a separate archive. or even more commonly, in a directory called 'docs'. you do not needlessly want to bloat your library's archive with the html and js files.

And why would you want to include the generated JavaDocs [html + js] in your project? As long the source code JavaDoc comments are in place, someone using your library will be able to see them by simply hovering over w/ the mouse in any of the modern IDE's

Update
As per nanda's comment below, I checked the same and he IS correct. In my project, I have actually attached Javadocs from the 'doc' folder to the archive to be able to view them on mouseover.