Update concepts/&str/about.md
Update concepts/&str/about.md

Co-authored-by: Eli Flanagan <10695c13cf85d13812306a923912e4c6d13ce56c@users.noreply.github.com>
exercism/xrust,exercism/xrust,petertseng/exercism-rust,petertseng/exercism-rust,petertseng/exercism-rust