add note about ios dropdown compat
add note about ios dropdown compat

BS3 commits: d18ba5083785052f37bc9e929fb315b144e88987

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