You need the full Cafe_SDK-2.12.13 package, the half a package on the wild site that you may of found is no good it needs to be the full SDK about 800MB in size, google it "pastebin". Extract that to your desktop and then put the ready made test.elf file which is easy to do into the makerpl folder, hold down shift key over the makerpl folder and open with command, type in first>
SET CAFE_ROOT=C:\Users....\wiiu\cafe_sdk-2_12_13\cafe_sdk-2_12_13-2
and then type in next>
makerpl64 -f -z9 -s <put in this bit what your original elf file is called without the "<> bits">.elf example
makerpl64 -f -z9 -s test.elf
Then just let it run to the end, your new .rpx file will be in the makerpl folder all compressed ready to work, I think some sort of little error does pop up in the end but if you leave it a while the compressed .rpx file is made up anyway
its really not that difficult, you don't need cygwin for this so if anyone tells you this its not true!