docs: display helm-diff install syntax for helm 3 or 4 (#3135)

This PR shows installation of helm-diff plugin depending on which
version of helm being used. If version 4 then --verify=false and if
version 3 no need for switch.

## Related issues
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## Type of Change
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## Testing
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## Additional Notes
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Signed-off-by: Benjamin Schmaus <bschmaus@nvidia.com>

Author: schmaustech

docs/getting-started/quick-start.md

@@ -67,6 +67,10 @@ The following tools must be installed on the machine that you will use to run `s
 The `helmfile` tool requires the `helm-diff` plugin. Install it as follows:
 
 ```bash
+# Helm v4
+helm plugin install https://github.com/databus23/helm-diff --verify=false
+
+# Helm v3
 helm plugin install https://github.com/databus23/helm-diff
 ```