docs: add missing description for warning/critical threshold flags

Author: wI2L

README.md

@@ -65,6 +65,7 @@ The following examples were produced from a brand-new Kubernetes cluster created
 
 Apart from the flags defined by the [`genericclioptions`](https://pkg.go.dev/k8s.io/cli-runtime/pkg/genericclioptions) package and some [logging flags](https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components), the following options are available with the plugin:
 - `--all-namespaces`, `-A`: List `VerticalPodAutoscaler` resources in all namespaces
+- `--critical-threshold`: Critical threshold of percentage difference for colored output. Default to `50`
 - `--namespace`, `-n`: If present, the namespace scope for the request
 - `--no-colors`: Do not use colors to highlight increase/decrease percentage values
 - `--no-headers`: Do not print table headers
@@ -76,6 +77,7 @@ Apart from the flags defined by the [`genericclioptions`](https://pkg.go.dev/k8s
 - `--show-namespace`: Show resource namespace as the first column
 - `--sort-columns`: Comma-separated list of column names for sorting the table. Any of: `cpu-diff` | `cpu-rec` | `cpu-req` | `mem-diff` | `mem-rec` | `mem-req` | `name` | `namespace` | `target`. Default to `namespace,name`
 - `--sort-order`: The sort order of the table columns. Either `asc` or `desc`. Default to `asc`
+- `--warning-threshold`: Warning threshold of percentage difference for colored output. Default to `20`
 
 To view the full list of available options, use the following command: