dracut.cmdline.7: add iso-scan/filename docs

dracut.cmdline.7.asc

@@ -109,6 +109,23 @@ resume=UUID=3f5ad593-4546-4a94-a374-bcfb68aa11f7
     the init system performs fsck before remount, you might want to use this
     option to avoid duplication.
 
+iso-scan/filename
+~~~~~~~~~~~~~~~~~
+
+Using iso-scan/filename with a Fedora/Red Hat/CentOS Live iso should just work
+by copying the original kernel cmdline parameters.
+
+[listing]
+.Example
+--
+menuentry 'Live Fedora 20' --class fedora --class gnu-linux --class gnu --class os {
+    set isolabel=Fedora-Live-LXDE-x86_64-20-1
+    set isofile="/boot/iso/Fedora-Live-LXDE-x86_64-20-1.iso"
+    loopback loop $isofile
+    linux (loop)/isolinux/vmlinuz0 boot=isolinux iso-scan/filename=$isofile root=live:LABEL=$isolabel ro rd.live.image quiet rhgb
+    initrd (loop)/isolinux/initrd0.img
+}
+--
 
 Misc
 ~~~~