docs: document single value as .query second argument

closes #1979

Author: anliting

Readme.md

@@ -661,6 +661,22 @@ connection.query({
 );
 ```
 
+If the query only has a single replacement character (`?`), and the value is
+not `null`, `undefiend`, or an array, it can be passed directly as the second
+argument to `.query`:
+
+```js
+connection.query(
+  'SELECT * FROM `books` WHERE `author` = ?',
+  'David',
+  function (error, results, fields) {
+    // error will be an Error if one occurred during the query
+    // results will contain the results of the query
+    // fields will contain information about the returned results fields (if any)
+  }
+);
+```
+
 ## Escaping query values
 
 **Caution** These methods of escaping values only works when the