Update doc/usage.md

HTML5 Boilerplate documentation link was incorrect.  
Merge pull request #687 from ShutterBrandon/patch-1

Update doc/usage.md
Root relative URLs
comment
added conditional
Fix (hack) for subdir installs
Merge pull request #688 from damianregan/relativeurls

Relative URL fixes
Fix for admin bar
Merge pull request #691 from damianregan/relativeurls

Fix for admin bar
Update lib/h5bp-htaccess

Removed redundant duplication comment. Just a tiny a tiny thing
Merge pull request #694 from adam-lynch/patch-2

Update lib/h5bp-htaccess
updated russian translation
Merge pull request #695 from sumkincpp/master

Updated russian translation
Merge remote-tracking branch 'upstream/master'