Bug 868928 - Expand bindings/README's section about context data. r=jbeatty
Bug 868928 - Expand bindings/README's section about context data. r=jbeatty

Expand README's section about context data to show the $var syntax and
data-l10n-args

zbraniecki/fluent.js,stasm/l20n.js,mail-apps/l20n.js,projectfluent/fluent.js,projectfluent/fluent.js,Pike/l20n.js,l20n/l20n.js,zbraniecki/l20n.js,zbraniecki/fluent.js,Swaven/l20n.js,Pike/l20n.js,mail-apps/l20n.js,projectfluent/fluent.js