Strengthen the warning about reusing certificates in the yaml installation.

[roberthbailey]

Also clarify the instructions a bit.

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking
/kind bug
/kind cleanup

/kind documentation

/kind feature
/kind hotfix

What this PR does / Why we need it:

Which issue(s) this PR fixes:

Closes #1064

Special notes for your reviewer:

[agones-bot]

Build Failed 😱

Build Id: 08dac6da-130e-49e6-a9e9-4a91cf491a76

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[roberthbailey]

TestFleetRollingUpdate/Use_fleet_Patch_true_25%_cycle_true failed on my documentation PR, which is clearly a flake. Restarting the e2e tests to see if I can get a clean run.

[agones-bot]

Build Failed 😱

Build Id: d8449e31-0866-4cbe-bda3-b256150126c6

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[zmerlynn]

This time it flaked on a unit test, TestControllerAllocator. :/

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gongmax, roberthbailey, zmerlynn

The full list of commands accepted by this bot can be found here.

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• OWNERS [roberthbailey]

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[google-oss-prow]

New changes are detected. LGTM label has been removed.

[agones-bot]

Build Succeeded 👏

Build Id: 436a5236-b53d-4142-865d-e97a1ecec959

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.32.0-b8260b4-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.32.0-b8260b4-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.32.0-b8260b4-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.32.0-b8260b4-amd64
• Linux C++ SDK (build): agonessdk-1.32.0-b8260b4-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.32.0-b8260b4-amd64.zip

A preview of the website (the last 30 builds are retained):

• https://b8260b4-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3167/head:pr_3167 && git checkout pr_3167
• helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.32.0-b8260b4-amd64