Add ISO patch guide

ISO.md

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+# Injecting a Rel Mod into an ISO
+* Install [Wiimms ISO Tools](https://wit.wiimm.de/) if you haven't already
+    * You may need to restart your computer after installation if the commands aren't working
+* Open the folder with your SPM ISO in a command prompt
+* Run the command `wit x ISONAMEHERE extracted`
+    * Replace ISONAMEHERE with the name of your ISO
+* Navigate to `extracted/DATA/files/`
+    * This should contain folders like `a`, `eff` and `font`
+* Create a folder named `mod`
+* Copy the rel for the mod into this folder and rename it `mod.rel`
+* In the same location as before, run the command `wit copy --align-files extracted mod.wbfs`
+    * Feel free to delete the `extracted` folder after this is done if you want to save storage space
+* Your ISO is now patched, return to the tutorial that linked you here for instructions on what to do next