How to generate scripts for a currently unsupported platform with `niminst`?
### Summary

Could someone explain (or refer to a documentation) how exactly to use `niminst` to generate build scripts for a currently unsupported platform? I need that for `csources` to begin with, and then for Nim.

### Description

The context: I have a PR for initial support of Darwin PowerPC (it is WIP, cannot be merged yet): https://github.com/nim-lang/csources_v1/pull/7
I did some manual patching back then, but it is not the right way to go. I was able to compile `niminst` from source on a arm64 Mac, but cannot figure out what to do to generate w/e needed for PowerPC.

### Alternatives

_No response_

### Examples

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### Backwards Compatibility

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### Links

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