[Trunk](https://trunkrs.dev) is a tool that allow you to build web apps
using Rust and webassembly, including compiling scss, and distributing
other assets.
Adds `craneLib.buildTrunkPackage`, a function that builds a Trunk
project returning a directory with the resulting dist files for that
project
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Co-authored-by: Ivan Petkov <ivanppetkov@gmail.com>
* add a section on customizing builds
* add an example for building custom command helpers
* add example on adding custom devShell env vars
* add local development section
