cleanig up section

Author: juslesan

docs/docs/usage/sdk/how-to-use.md

@@ -29,6 +29,8 @@ If using Node.js you can import the library with:
 const { StreamrClient } = require('@streamr/sdk');
 ```
 
+### Cleaning up
+
 After the StreamrClient is no longer needed or the process is shutting down it is very important to destroy the StreamrClient:
 
 ```js