Fix a typo for the 'delete' instruction (#551)

The description for the delete logic should be: implement the logic for the 'delete' instruction rather than  ...  'update' instruction

docs/intro/quick-start/program-derived-address.md

@@ -599,7 +599,7 @@ The `Delete` struct defines the accounts required for the `delete` instruction:
 </AccordionItem>
 </Accordion>
 
-Next, implement the logic for the `update` instruction.
+Next, implement the logic for the `delete` instruction.
 
 ```rs filename="lib.rs"
 pub fn delete(_ctx: Context<Delete>) -> Result<()> {