fix/documentation(#17) : Fix incorrect link

[jinwoolee]

This PR add a https protocol text

[egli]

Thanks for the PR. It does indeed fix the immediate problem, but only until we build the html documentation again next time from the texinfo sources.

Would you mind providing a PR for the texinfo sources themselves? All you really have to do is to change the URLs in the @uref{} tags

So @uref{www.viewplus.com} needs to be changed to @uref{https://www.viewplus.com}

These changes need to be applied to liblouis.texi and to liblouisutdml.texi