Update provider name to be a variable

Co-authored-by: Cong Liu <[email protected]>

Author: rahulgurnani

site-src/guides/index.md

@@ -276,7 +276,7 @@ A cluster with:
    export PROVIDER_NAME=none #  See [README](https://github.com/kubernetes-sigs/gateway-api-inference-extension/blob/main/config/charts/inferencepool/README.md#configuration) for valid configurations
    helm install vllm-llama3-8b-instruct \
    --set inferencePool.modelServers.matchLabels.app=vllm-llama3-8b-instruct \
-   --set provider.name=PROVIDER_NAME \
+   --set provider.name=$PROVIDER_NAME \
    --version v0.3.0 \
    oci://registry.k8s.io/gateway-api-inference-extension/charts/inferencepool
    ```