The MySQL++ documentation is split into two parts:
User Manual (HTML, online), or in PDF form: userman.pdf (403 kiB, 2019.07.21) Both versions have the same content, generated from the same sources. The PDF is prettier, but the HTML version has hyperlinks to the reference manual where appropriate.
Reference Manual (HTML, online only)
If you want a local copy of the HTML documentation, it is included in the main source tarball.