[jsh9]

Summary

The README now opens with what PySeismoSoil does, and the published docs homepage stays a copy of that README.

• Sections 1.1–1.3 describe linear, equivalent-linear, and nonlinear site response, the sediment velocity model, and the SAG19 site factors. Those descriptions were checked against Chapters 2–4 of Shi (2019) and corrected where they disagreed with the thesis (see below).
• Section 1.4 lists five ground-motion utilities.
• PySeismoSoil.__version__ is read from the installed package metadata (importlib.metadata) instead of a hard-coded string.
• A pre-commit hook, copy_readme, copies README.md to docs/source/index.md. Sphinx reads that file with MyST, and the hook appends a hidden table of contents so the class and module pages stay in the sidebar.
• Paper links use authors.library.caltech.edu where a CaltechAUTHORS record exists. The 2019 dissertation is on thesis.caltech.edu, which is where that record lives.
• The license link points at the file on main. The supported-Python-versions section is removed.

Corrections against the thesis:

• Equivalent-linear analysis is not described as the method for moderate shaking. Chapter 3 finds that it underestimates stronger motion, especially above about 5 Hz, once the shear strain exceeds about 0.04% (surface PGA on the order of 0.05 g).
• MKZ is the Matasović and Vucetic (1993) modification of the Kondner and Zelasko (1963) hyperbola. Unlike HH, its shear stress is not bounded by the soil strength.
• z₁ is the depth to bedrock (where V_S first reaches 1,000 m/s), not a depth to soil. The SVM itself is a V_S30 model for California basin sediments, supported from about 173 m/s to 1,000 m/s.
• The site-factor database (SAG19) has both a nonlinear version and an equivalent-linear version. Each factor is a Fourier spectral ratio: amplitude is amplification, and phase is the frequency-dependent delay. The reference site has V_S30 = 1,046 m/s.

Test

• pre-commit run -a passes, including check-notebooks-were-run.
• make html in docs/ succeeds on the previous homepage setup. This commit only changes the README text that the same hook copies into docs/source/index.md.