Clarify nesting in grid example
Clarify nesting in grid example

BS3 commits: af1ba5cf74fb695674a166c3c6883bf62e91ceda

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