The required packages should not be in the build scripts, because
they are distro-dependent, they are in bld_prepare.sh .

OK, I see that now. Some of the email gets put in my Spam folder so I have to keep checking (like configure.ac).

If the HTML manual is copied to the proper place, it will be included
in the AppImage.

Well, if you run bld_appimage.sh from the top after having run "make clean" those files will not be in bin/doc . This is not a problem for me at all so I think just echoing a comment to remind a user would be more than sufficient.