npm install Handlebars
Um, seriously that's it. The index.js file has a couple of tidbits that are helpful to be aware of.
1. Output from compilation is piped directly into the Handlebars compiler.
2. Data from Sanity IO that will be compiled by Handlebars -> HTML needs to be escaped. Triple brackets are used to enclose HTML that will be escaped, e.g.{{{some.val}}}
2. a. The triple brackets can be enclosed in square brackets, e.g. [{{{some.val}}}]. The Jackle compiler syntax will pick this up from the JS Jackle template and will compile that to standard HTML.