Polish examples and README quickstart

[krystophny]

Summary

• Add examples/run_example.sh as a self-contained demo script (downloads test data, runs SIMPLE, prints confined fraction)
• Fix stale f90wrap version pin in README (was 0.2.16, now unpinned)
• Clarify that simple.in is the quickstart and simple_full.in the full parameter reference
• Replace stale "Comparing Commits" section with reference to test/golden_record/golden_record.sh

Test plan

• make CONFIG=Fast builds successfully
• examples/run_example.sh downloads data and runs SIMPLE, producing confined_fraction.dat
• No existing tests affected (documentation/example changes only)