[kde-doc-english] Minor errors in Klipper handbook

[Bruce]

Hi.
  - in the Contents, the list stops at 'Credits and Licence' while Next 
is the 'Appendix A. Installation' of Klipper and so on.

  - the 'KDE Docs Team' link did not work. The application that it 
attempts to start is /opt/thunderbird /thunderbird which does not exist 
on my Kubuntu 14.04. To send this email I needed to create a link to 
thunderbird there.

Cheers, Bruce