Add a note in documentation regarding systemd mode

[souleb]

No description provided.

[github-actions]

Thanks for your PR,
To run vendors CIs, Maintainers can use one of:

• /test-all: To run all tests for all vendors.
• /test-e2e-all: To run all E2E tests for all vendors.
• /test-e2e-nvidia-all: To run all E2E tests for NVIDIA vendor.

To skip the vendors CIs, Maintainers can use one of:

• /skip-all: To skip all tests for all vendors.
• /skip-e2e-all: To skip all E2E tests for all vendors.
• /skip-e2e-nvidia-all: To skip all E2E tests for NVIDIA vendor.
  Best regards.

[coveralls]

Pull Request Test Coverage Report for Build 11467893352

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.007%) to 45.003%

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Files with Coverage Reduction	New Missed Lines	%
controllers/drain_controller.go	1	68.06%

Totals
Change from base Build 11441395281:	-0.007%
Covered Lines:	6660
Relevant Lines:	14799

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💛 - Coveralls