[goroyabu]

Summary

• Install the upstream roff manual source as share/man/man1/f2c.1 through GNUInstallDirs.
• Document local manual lookup, including MANPATH handling for custom prefixes.
• Verify the installed source, rendered sections, install manifest, and uninstall behavior in online and offline CI paths.

Related Issue

Closes #61

Verification

• cmake --build build --parallel
• ctest --test-dir build --output-on-failure — 63/63 tests passed.
• Verified the installed manual source, .TH F2C 1 declaration, install manifest entry, and rendered NAME, SYNOPSIS, and DESCRIPTION sections with mandoc.
• Verified man f2c using the staged manual directory through MANPATH.
• Verified a strict offline build and installation with an overridden CMAKE_INSTALL_MANDIR.
• Verified the downstream CMake example and incremental regeneration workflow.
• Verified uninstall removes the manual page while preserving an unrelated staged file.

Linux rendering remains covered by the GitHub Actions matrix because the local verification environment is macOS.

Impact

Installs a new local f2c(1) manual page. Converter behavior, runtime behavior, and existing public CMake targets are unchanged.

Documentation

The README now lists the installed manual page and documents man f2c and custom-prefix MANPATH usage. The browser-accessible upstream manual link remains available.

Checklist

• The change is focused on one coherent maintenance outcome.
• Relevant local verification has been run and reported above.
• User-facing workflows and supported behavior are documented when changed.
• No downloaded upstream archives, extracted vendor sources, build outputs,
  or generated files were committed unintentionally.