Rewrite README to match wrapper documentation standard.
- Remove pbench references
- Add missing general_setup options (--tools_git, --sysname, --sys_type, --run_user, --host_config, --home_parent, --tuned_setting, --use_pcp)
- Follow the same structure as autohpl-wrapper README (Description, Command-Line Options, What the Script Does, Dependencies, Examples, Return Codes, Notes)
- Document the actual behavior of the linpack_run script accurately
Rewrite README to match wrapper documentation standard.