update doc that should support mysql.param

[isdaniel]

我發現 nacos 的 k8s yaml template 有使用且支援 mysql.param, 如果是使用这个 template conifgmap 应该也可以使用 "mysql.param" 来调整 parameter.

            - name: MYSQL_SERVICE_PASSWORD
              valueFrom:
                configMapKeyRef:
                  name: nacos-cm
                  key: mysql.password
            - name: MYSQL_SERVICE_DB_PARAM
              valueFrom:
                configMapKeyRef:
                  name: nacos-cm
                  key: mysql.param

https://github.com/nacos-group/nacos-k8s/blob/v1.0.0/helm/templates/statefulset.yaml#L134-L138
https://github.com/nacos-group/nacos-k8s/blob/v1.0.0/helm/templates/configmap.yaml

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