Warn about IE8 + Respond.js + file:// problem in examples. JS docs: add cross-reference to Getting Started mobile modal section. missed change

BS3 commits: eb4a92bfedde23729bc812b9d6abe704bd8bca59,
0806819bcf2e4c763f90709093f573cc02f16df2
Warn about IE8 + Respond.js + file:// problem in examples

BS3 commits: eb4a92bfedde23729bc812b9d6abe704bd8bca59