Merge pull request #1440 from kegsay/patch-1

Improve developer build instructions

Author: ganfra

docs/_developer_onboarding.md

@@ -142,6 +142,11 @@ So for example to build the sdk against aarch64-linux-android target and copy th
 ./scripts/build.sh -p [YOUR MATRIX RUST SDK PATH] -t aarch64-linux-android -o [YOUR element-x-android PATH]/libraries/rustsdk/matrix-rust-sdk.aar
 ```
 
+Troubleshooting:
+ - You may need to set `ANDROID_NDK_HOME` e.g `export ANDROID_NDK_HOME=~/Library/Android/sdk/ndk`.
+ - If you get the error `thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', .cargo/registry/src/index.crates.io-6f17d22bba15001f/cargo-ndk-2.11.0/src/cli.rs:345:18` try updating your Cargo NDK version. In this case, 2.11.0 is too old so `cargo install cargo-ndk` to install a newer version.
+ - If you get the error `Unsupported class file major version 64` try changing your JVM version. In this case, Java 20 is not supported in Gradle yet, so downgrade to an earlier version (Java 17 worked in this case).
+
 Finally let the `matrix/impl` module use this aar by changing the dependencies from `libs.matrix.sdk` to `projects.libraries.rustsdk`:
 
 ```groovy