Update security_groups.md

[zhming0]

This PR updates security_groups.md in order to clear some confusions that developers might encounter when they see the name of "securityGroupOverride".

Specifically, Override implies that the passed in security group will be the source of truth, but in reality the passed in security group will be modified.
The awareness of this tiny detail will potentially prevent unwanted changes to some shared security groups.

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Hi @zhming0. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[rifelpet]

/ok-to-test

[rifelpet]

hmm i'm looking at the site preview and i don't think the markdown list is being formatted correctly. you might need to indent the This is due to... line to match the indentation of the line above it. I don't know for sure, the docs aren't super clear...

[zhming0]

@rifelpet thanks for pointing it out. I didn't know we have this preview site feature, fancy 👍 .

I tweaked it a little bit and it looks normal now.

[zhming0]

/retest

[rifelpet]

look great, thanks!

/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rifelpet, zhming0

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