add document about mkisofs and an example .mkisofsrc

doc/.mkisofsrc

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+# Sample .mkisofsrc file for Neo-Geo CD images
+# set Abstract, Bibliography, Copyright to the existing files
+ABST=ABS.TXT
+BIBL=BIB.TXT
+COPY=CPY.TXT
+# optional/editable fields (remember to uncomment)
+# Application Identifier (128 chars)
+#APPI=
+# Preparer of CDROM (128 chars)
+#PREP=
+# Publisher of CDROM (128 chars)
+#PUBL=
+# System Identifier (32 chars)
+#SYSI=
+# Volume Identifier (32 chars)
+#VOLI=
+# Volume Set Name (128 chars)
+#VOLS=

doc/mkisofs.txt

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+The mkisofs tool is used to create ISO images.
+https://wiki.neogeodev.org/index.php?title=ISO_generation
+
+The example from the wiki:
+mkisofs -iso-level 1 -o neogeocd.iso -pad -N -V "NGCDTEST" P1.PRG M1.Z80 SPR.SPR S1.FIX V1.PCM IPL.TXT ABS.TXT BIB.TXT CPY.TXT
+
+The setup I prefer is something like this:
+mkisofs -iso-level 1 -o neogeocd.iso -pad -N -V "NGCDTEST" -path-list pathlist.txt
+
+where pathlist.txt is a file containing a list of directories and filenames to be
+added to the filesystem. This way, you don't have to type a bunch of files on the
+command line.
+
+In addition, I have provided an example .mkisofsrc file that can be used/edited.