docs: add best practice for fonts persistence

Author: Jackie1210

README.md

@@ -315,7 +315,12 @@ await satori(
 )
 ```
 
-Multiple fonts can be passed to Satori and used in `fontFamily`.
+Multiple fonts can be passed to Satori and used in 
+
+> [!TIP]
+> We recommend you define global fonts instead of creating a new object and pass it to satori for better performace. [Read it for more detail](https://github.com/vercel/satori/issues/590)
+
+`fontFamily`.
 
 #### Emojis