Follow important `parachain-staking` upstream changes

[Kailai-Wang]

Context

As the staking is an important on-chain feature, I suggest that we:

• add a README to briefly describe the background information of this pallet and track the upstream revision history (e.g. which upstream commit are we based on?)
• follow upstream changes regularly (~ once per month) and integrate the important features/bug-fixes to our implementation

---

✔️ Please set appropriate labels and assignees if applicable.

[Kailai-Wang]

I see moonbeam's repo has been updated actively - can you double-check it @wangminqi ?

Ideally we can have a (brief) monthly summary about the main upstream changes and if we should follow them.

[Kailai-Wang]

friendly reminder @wangminqi :)

[wangminqi]

Checking. Do notice some small bugs worth adoption
#1450