dh_installinfo is a debhelper program that is responsible for installing info files and registering the files it installs with install-info.
It determines some information about the info files by parsing them, in particular, it looks at the INFO-DIR-SECTION line to determine what section the info file belongs in.
Any filenames specified as parameters will be installed into the first package dh_installinfo is told to act on. By default, this is the first binary package in debian/control, but if you use -p, -i, or -a flags, it will be the first package specified by those flags.
Files named debian/package.info can list other files to be installed.
Install all files specified by command line parameters in ALL packages acted on.
Do not modify postinst/prerm scripts.