[DatTools] Add skip for first cascade diff output

Flag enables first output DAT to skip output for instances where the first DAT is always known or is very large

SabreTools.Helper/Data/Build.cs

@@ -175,6 +175,7 @@ Options:
 		-b, --bare		Don't include date in automatic name
 		-c, --cascade		Enable cascaded diffing
 			-ip, --inplace		Enable inplace, cascaded diff
+			-sf, --skip		Skip output of first DAT
 	-gn=, --game-name=	Filter by game name
 	-rn=, --rom-name=	Filter by rom name
 	-rt=, --rom-type=	Filter by rom type