Document backing store

Is your feature request related to a problem? Please describe.
When I first used this SDK, I modified objects that were returned but just for the needs of my script, with no intention of pushing back to the API the modifications. It didn't work properly and I had a couple of issues that I didn't understand at first, until I noticed that this SDK uses a notion of "backing store". I didn't dig deeper what it was but now I understand thanks to this description in the Java Graph SDK for the "backing store" and "dirty" mechanisms which I believe are the same as in this Python SDK.

Describe the solution you'd like
If it's indeed the same thing, please raise awareness about it in the README (or elsewhere) to reduce confusion

Describe alternatives you've considered
Perhaps I could have spent more time and managed to find the article myself, or this https://learn.microsoft.com/en-us/openapi/kiota/models#backing-store

檢閱 README 以及連結的 Microsoft Graph Java 和 Kiota backing store 說明。確認 Python SDK 的 backing store 和 dirty mechanisms 如何運作，然後在 README 或其他適當的位置記錄這些內容，讓使用者了解何時會追蹤傳回物件的變更，或何時會將這些變更傳回 API。