Add a doc about maintaining a node

[fgksgf]

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[Oreoxmt]

@fgksgf fgksgf#9 PTAL

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-09-24 03:13:37.166162357 +0000 UTC m=+412827.236656035: ☑️ agreed by Oreoxmt.

[Oreoxmt]

/cc @liubog2008