docs: add more documentation regarding util.inspect

Author: dougwilson

README.md

@@ -6,7 +6,23 @@
 [![Test Coverage][coveralls-image]][coveralls-url]
 [![Gratipay][gratipay-image]][gratipay-url]
 
-Development-only error handler middleware
+Development-only error handler middleware.
+
+This middleware is only intended to be used in a development environment, as
+the _full error stack traces and internal details of any object passed to this
+module_ will be sent back to the client when an error occurs.
+
+When an object is provided to Express as an error, this module will display
+as much about this object as possible, and will do so by using content negoiation
+for the response between HTML, JSON, and plain text.
+
+  * When the object is a standard `Error` object, the string provided by the
+    `stack` property will be returned in HTML/text responses.
+  * When the object is a non-`Error` object, the result of
+    [util.inspect](https://nodejs.org/api/util.html#util_util_inspect_object_options)
+    will be returned in HTML/text responses.
+  * For JSON responses, the result will be an object with all enumerable properties
+    from the object in the response.
 
 ## Install
 
@@ -23,9 +39,6 @@ var errorhandler = require('errorhandler')
 ### errorhandler(options)
 
 Create new middleware to handle errors and respond with content negotiation.
-This middleware is only intended to be used in a development environment, as
-the full error stack traces will be sent back to the client when an error
-occurs.
 
 #### Options