Add a Linux/openSUSE FAQ about 'zypper install' not working

[HoussemNasri]

Refs JabRef/jabref#10603

Sometimes when you are on an openSUSE Linux system and try to install Jabref RPM with zypper install jabref-...rpm you get this error Problem reading the RPM header of JabRef-....rpm. Is it an RPM file? No valid arguments specified

The error can be fixed by following these instructions:

1. Create a directory for RPMs .e.g. ~/.rpm.
2. Add the directory as a repository.
3. Try again the installation from inside the directory that you created.

Read this for more context.