Add one line note about 0000-00-00 date/datetime (#783)

Fixes #741

Signed-off-by: INADA Naoki <songofacandy@gmail.com>

README.md

@@ -259,6 +259,7 @@ Default:        false
 ```
 
 `parseTime=true` changes the output type of `DATE` and `DATETIME` values to `time.Time` instead of `[]byte` / `string`
+The date or datetime like `0000-00-00 00:00:00` is converted into zero value of `time.Time`.
 
 
 ##### `readTimeout`