APP_BUILD iOS Workspace File Name Outdated

In this file:
https://github.com/touchlab/KaMPKit/blob/main/docs/APP_BUILD.md

The iOS instructions are just slightly outdated. Under section **3) Build iOS**, it references: `KaMPKitiOS.xcworkspace`.

This file has now been renamed to: `KaMPKitiOS.xcodeproj`:
https://github.com/touchlab/KaMPKit/tree/main/ios/KaMPKitiOS.xcodeproj

🎉 🎉 🎉 