Add openSUSE reference.

index.md

@@ -72,6 +72,9 @@ You can try it now using Docker:
 * On <a href="https://fedoraproject.org">Fedora</a> based systems:<br/>
 `dnf install diffoscope`
 
+* On <a href="https://opensuse.org">openSUSE</a>:<br/>
+`zypper in diffoscope`
+
 * On <a href="https://archlinux.org">Arch Linux</a>:<br/>
 `pacman -S diffoscope`