update note for Preview APIs in readme

Now that the preview api accept headers are taken care of in the library
let the user know that it's mostly taken care of but leave example in
case an accept header needs to be manually added.

README.md

@@ -174,8 +174,8 @@ $ npm test test/issuesTest.js
 
 ## Preview APIs
 
-Some APIs are in a preview period and require a custom `Accept` header.  
-See [examples/getReactionsForIssue.js](https://github.com/mikedeboer/node-github/blob/master/examples/getReactionsForIssue.js) for an example.  
+Accept headers for the preview APIs should be taken care of behind the scenes, but in the event a preview endpoint isn't working, see [here](https://github.com/mikedeboer/node-github/blob/master/examples/getReactionsForIssue.js) for an example on how to add the required custom accept header.
+
 For updates on endpoints under preview, see https://developer.github.com/changes/.
 
 | Preview API         | Accept header val                               |