feat: expand read-only section

Author: Timongcraft

src/content/docs/paper/dev/api/pdc.md

@@ -205,6 +205,9 @@ container.set(key, UUIDDataType.INSTANCE, uuid);
 
 Certain classes, like `ItemStack` or [`OfflinePlayer`](jd:paper:org.bukkit.OfflinePlayer), provide a read-only view of their PDC.
 In contrast to `ItemStack`, `OfflinePlayer` does <u>not</u> provide any way to modify the underlying container.
+This is because the OfflinePlayer is directly read from disk and would require a blocking file operation.
+Mutable objects, like the `PersistentDataHolder#getPersistentDataContainer()`, generally need to be re-saved even without modification or monitored.
+That's why it's better to use unmodifiable "views" for read-only operations.
 
 :::