Update gen-apply-cluster.md

[lamking]

Here, the -o parameter should be used

[cla-assistant]

All committers have signed the CLA.

[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
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[sealos-ci-robot]

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✅ Successful	365
⏳ Timeouts	0
🔀 Redirected	0
👻 Excluded	800
❓ Unknown	0
🚫 Errors	0

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[fanux]

@lamking sign the CLA~

[lamking]

@lamking sign the CLA~

I've clicked agree but it still says not signed yet

[lamking]

@lamking sign the CLA~

Progress shows "Please set the milestone!", but I don't know how to set the milestone.

[bxy4543]

@lamking sign the CLA~

Progress shows "Please set the milestone!", but I don't know how to set the milestone.

@lamking Thanks for the contribution, the CLA has been signed and I will merge the commit.

[lamking]

@lamking sign the CLA~

Progress shows "Please set the milestone!", but I don't know how to set the milestone.

@lamking Thanks for the contribution, the CLA has been signed and I will merge the commit.

OK thanks~
sealos is a cool app. !!!