Update README.md for fsGroupPolicy

[cdm-arm]

Since version 4.0.0 enableFSGroupPolicy is set to true

What type of PR is this?
/kind documentation

What this PR does / why we need it:
Update docu to reflect change in helm chart

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:
Fixes #652

Updated documentation for fsGroupPolicy

[linux-foundation-easycla]

• ❌ - login: @cdm-arm / name: Arne Moor . The commit (fb30c3c) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

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[k8s-ci-robot]

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[APPROVALNOTIFIER] This PR is NOT APPROVED

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[coveralls]

Pull Request Test Coverage Report for Build 8750150199

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 78.915%

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Totals
Change from base Build 8731467405:	0.0%
Covered Lines:	887
Relevant Lines:	1124

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💛 - Coveralls

[andyzhangx]

@cdm-arm can you sign the cla first? thanks.