Docs: add missing example code code for `kbd` after 13351.
Docs: add missing example code code for `kbd` after 13351.

BS3 commits: bae2c55a52cb873f71037651c96deb7553d429e9

aaroncnhk/todc-bootstrap,mozillo/todc-bootstrap,todc/todc-bootstrap,2947721120/todc-bootstrap,todc/todc-bootstrap,2947721120/googlebt4,up2vs/todc-bootstrap,todc/todc-bootstrap,ztx1491/todc-bootstrap