Please write a proper guide on using buildFHSEnv as some binaries only work with that (not all can be patched)

[adam248]

Learning goals

Describe when and when not to use buildFHSEnv for official contributions, but also general guide on how to use it and why it is considered a "shortcut" most times in the Nix eco system.

Prerequisites
This is more a standalone, so maybe more in the guides section?

Outline

Mainly just the use of FHSEnv in packaging or patching software to get working. How to just get unique software working (that is not already packaged in nixpkgs)

Prior art

https://discourse.nixos.org/t/trying-to-contribute-to-nixpkgs-but-only-buildfhsenv-works-for-binary/36579

Willing to help?

Sure, just ping me if you need me to proof read.

Priorities

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