improve creating dataset document

Creating a new dataset normally has two steps. At first, we should initiate a folder to be ready to upload files. It easily got confused for newbies.

Author: rocLv

README.md

@@ -304,6 +304,8 @@ Example:
 
 ##### Create a new dataset
 
+If you want to create a new dataset, you need to initiate metadata file at first. You could fulfill this by running `kaggle datasets init -p FOLDER`.
+
 ```
 usage: kaggle datasets create [-h] [-p FOLDER] [-u] [-q] [-t]