Add iOS small troubleshooting guide

[dfernandezm]

Context

With multiple versions of Java, JAVA_HOME may not point to Java 11 or later. This makes the iOS build break.
Also small basic tips for beginners like me in Xcode (cleaning derived sources folder to avoid constant build failures for example).

Also worth indicating the steps I needed to get Android working with M1 (needed to uninstall the emulator SDK that I brought in from my Intel backup)

[dfernandezm]

@gchristov I plan to add this one with my steps at the bottom of README

[gchristov]

Sounds good 👌