add comments

examples/postbin.js

@@ -3,8 +3,8 @@
 var request = require('../');
 request({
     url: 'https://postb.in/1588134650162-6019286897499?hello=world'
-    //headers: { 'user-agent': false }
-    //headers: { 'user-agent': 'test/1.0' }
+    //headers: { 'user-agent': false } // remove
+    //headers: { 'user-agent': 'test/1.0' } // overwrite
     //userAgent: 'test/1.1' // not presently implemented
 })
     .then(function(resp) {