document that multiple navbars aren't supported by default; addresses 10824
document that multiple navbars aren't supported by default; addresses 10824

BS3 commits: 5528c6501cd0f382289630665fa77394146ea68c

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