Polish helm related docs

[Huanli-Meng]

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[Huanli-Meng]

@Anonymitaet, please help review.

[lukestephenson]

Hello. I'm not sure if it is related to this PR, but in 2.5.2 of the docs, the section to "Run Pulsar in Kubernetes" has disappeared from "Get started".

Compare this to the previous version 2.5.1 and it is present

[Huanli-Meng]

@lukestephenson , Thanks for your feedback. I will check the doc and fix it as soon as possible.