Improve development setup instructions

I'm trying to build Pkl on Ubuntu 22.04/WSL 2.0.14. (I'd prefer to build directly in Windows but ran into https://github.com/apple/pkl/issues/20 and failing tests.) After reading through `DEVELOPMENT.adoc`, I have the following questions:

What does "Setup Gradle on your system" entail? (`./gradlew build` seems to work fine without further setup.)

How do I make `./gradlew buildNative` work? Currently, task `:pkl-cli:alpineExecutableAmd64` fails with:
```
/usr/bin/ld: cannot find -lz: No such file or directory
```

Further up I see:
```
[7/7] Creating image... (0.0s @ 1.86GB)
Fatal error: java.lang.RuntimeException: There was an error linking the native image: Linker command exited with 1

Based on the linker command output, possible reasons for this include:
1. It appears as though libz:.a is missing. Please install it.
```

Installing package `zlib1g-dev`, which contains `/usr/lib/x86_64-linux-gnu/libz.a`, didn't solve the problem.

The good news is that after tinkering with the build scripts to exclude the Alpine build and test tasks, `./gradlew build buildNative` succeeded. So I think I'm pretty close...

Start with DEVELOPMENT.adoc and the ./gradlew buildNative task, then inspect the build scripts that select the Alpine executable and test tasks. Reproduce the linker failure on Ubuntu 22.04/WSL and compare it with the successful build after excluding Alpine tasks. Done means the development setup instructions explain Gradle setup, native-build prerequisites, and the relevant limitation or workaround.

Written by the indexing model from the issue text.