Oops, I didn't check that. I went straight to the repository and the website. It might be worth adding that link somewhere in the documentation. I see it now on your Downloads page but it doesn't seem to be mentioned anywhere else.
BTW, the .zip file can't be installed via Library Manager, but it can be installed via Sketch > Include Library > Add .ZIP Library.... Library Manager makes installation and updates especially of libraries even easier but you need to have an Arduino IDE compatible library in a repository, then simply submit a request for it to be added to the index. Details here:
There is a minor problem with the formatting of your keywords.txt file. The field separators must be a single true tab, not multiple tabs or spaces. If you have that file on GitHub anywhere, I'm happy to submit a pull request. Otherwise, you can just refer to the relevant section of the Arduino library specification: