Re-adds Wii U nightly build link (#2951)

Now that we have Wii U building again, re-add the nightly link for it to the README.

README.md

@@ -103,6 +103,7 @@ If you want to playtest a continuous integration build, you can find them at the
 * [Linux (performance)](https://nightly.link/HarbourMasters/Shipwright/workflows/generate-builds/develop/soh-linux-performance.zip) _(requires `glibc 2.35` or newer, but will be more performant than the compatibility build.)_
 * [Linux (compatibility)](https://nightly.link/HarbourMasters/Shipwright/workflows/generate-builds/develop/soh-linux-compatiblity.zip) _(compatible with most Linux distributions, but may not be as performant as the performance build.)_
 * [Switch](https://nightly.link/HarbourMasters/Shipwright/workflows/generate-builds/develop/soh-switch.zip)
+* [Wii U](https://nightly.link/HarbourMasters/Shipwright/workflows/generate-builds/develop/soh-wiiu.zip)
 
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