Update readme.md

Author: sindresorhus

readme.md

@@ -217,7 +217,7 @@ queryString.parse('?isAdmin=true&flagged=true&isOkay=0', {
 //=> {isAdmin: 'true', flagged: true, isOkay: false}
 ```
 
-Note: The `'boolean'` type will also convert `'0'` and `'1'` string values to booleans.
+Note: The `'boolean'` type also converts `'0'` and `'1'` to booleans, and treats valueless keys (e.g. `?flag`) as `true`.
 
 - `'string'`: Parse `phoneNumber` as a string (overriding the `parseNumbers` option):