If there are no html files in the "manual" directory and there is no
"manual.html" file, it means that you have either checked out the source
repository on a non-release branch or the packager messed up.

In either case, if you have "docbook2html" installed, you should be able
to build the manual with one of the following:

docbook2html -o manual manual.docbook.sgml

or

docbook2html -u manual.docbook.sgml && mv manual.docbook.html manual.html