Better comments

src/index.js

@@ -3,13 +3,18 @@ const differenceInMilliseconds = require('date-fns/difference_in_milliseconds');
 const addSeconds = require('date-fns/add_seconds');
 const parse = require('parse-headers');
 
+// Returns boolean for whether or not the cache has expired
 const expired = headers => isPast(expired.on(headers));
 
+// Return ms until cache expires
 expired.in = headers => differenceInMilliseconds(expired.on(headers), new Date());
 
+// Returns date when cache will expire
 expired.on = headers => {
+	// Parse headers if we got a raw string
 	headers = (typeof headers === 'string') ? parse(headers) : headers;
 
+	// Date from headers
 	const originDate = new Date(headers.date);
 
 	// Get max age ms