Document and regenerate plink_simulated phenotype sidecars

[lyh970817]

PR checklist

• I read the test-data specifications
• I tried testing my module with available data and there is no compatible data in test-datasets
• If I added data: I described the new files on the root README.md
• If I modified data: I checked whether the root README.md is still up-to-date
• I made sure to submit the smallest dataset possible (e.g. try .tar.gz for larger directories)

Summary

This draft PR is a follow-up to the earlier REGENIE test-datasets contribution in nf-core/test-datasets PR #1919.

PR #1919 added the plink_simulated REGENIE phenotype and covariate sidecars, but it did not fully document those files in the repository metadata. This follow-up updates the root README.md, adds command-focused generation notes to data/genomics/homo_sapiens/popgen/README.md, and rewrites the REGENIE sidecars in a deterministic space-delimited form so the documented commands reproduce the checked-in files.

Rationale

The original REGENIE dataset PR is already closed and merged, so this needs to be submitted as a separate follow-up branch instead of amending the old submission.

Opening a new PR keeps the corrective scope explicit:

• document the existing plink_simulated phenotype-related files in the root inventory
• record reproducible shell commands for generating plink_simulated.phe and the REGENIE sidecars in the popgen folder README
• document that the *_phenoname.phe files use named phenotype columns (Phenotype, QuantitativeTrait, BinaryTrait)
• align the checked-in REGENIE sidecar contents with those documented deterministic commands using space-delimited output to match the existing plink_simulated.fam / plink_simulated.phe style

Additional documentation-only note

This PR also documents the pre-existing plink_simulated_phenoname.phe file for completeness in the root inventory and popgen README.
That file predates PR #1919 and is not being changed by this follow-up; its mention here is a pure documentation addition so the phenotype-file section is complete.

Files touched

• README.md
• data/genomics/homo_sapiens/popgen/README.md
• data/genomics/homo_sapiens/popgen/plink_simulated_binary_phenoname.phe
• data/genomics/homo_sapiens/popgen/plink_simulated_covariates.txt
• data/genomics/homo_sapiens/popgen/plink_simulated_quantitative_phenoname.phe

Related PRs

• Previous dataset PR: Add REGENIE phenotype and covariate sidecars for plink_simulated #1919
• Companion modules PR: Add REGENIE step1 and step2 modules with Wave containers and expanded GWAS tests modules#10800