docs: introduce wicked-sqlc architecture

[Stumble]

Summary

Introduce wicked-sqlc with a concise architecture overview, a small working
example, and links to the guide and bookstore. Preserve the original upstream
README at the end.

Architecture and Key Decisions

• Explain the compiler, GenerateRequest/WickedMetadata contract, and dedicated
  wicked backend against the implementation now on main.
• Clarify that query options use ordinary comments and the backend is bundled in
  one binary, selected by sql_package: wpgx.
• State that wicked-sqlc is regularly rebased onto upstream releases without
  tying the architecture to one version.
• Keep the original upstream README unchanged below the fork introduction,
  including its badges, links, and sponsors. No implementation or guide changes.

Risks and Remaining Work

No known issues. Architecture claims were checked against the compiler,
shim/proto, dispatcher, in-process handler, and backend.

Breaking Changes

None; documentation only.

Database Migrations

None.

Verification

• git diff --check origin/main passed; only README and its changelog changed.
• make -n install confirmed the build command without replacing the installed
  binary. No make lint-fix target exists.
• node /tmp/sqlc-readme-validation.1zZzaq/verify.mjs passed relative-link,
  code-fence, and exact README YAML/SQL fixture checks. It also verifies
  version-neutral wording and byte-for-byte preservation of the upstream README.
• In that temporary fixture, the verified main-equivalent binary passed both
  sqlc generate and sqlc diff. Inspected the generated timeout, cache, replica,
  and load/dump code.
• Full local runtime/E2E tests were not rerun for a Markdown-only change. Existing
  GitHub workflows run on this PR.

Merge Order

None; based directly on current main.

Related PRs

Follows the merged architecture work in #17.