Added Open Service Broker reference link (kubernetes#17721)

`https://openservicebrokerapi.org/` contains information such as `what are service brokers?`, how they work, building services for Kubernetes using `Open Service Broker API` etc.

content/en/docs/concepts/overview/what-is-kubernetes.md

@@ -77,7 +77,7 @@ Kubernetes:
 
 * Does not limit the types of applications supported. Kubernetes aims to support an extremely diverse variety of workloads, including stateless, stateful, and data-processing workloads. If an application can run in a container, it should run great on Kubernetes.
 * Does not deploy source code and does not build your application. Continuous Integration, Delivery, and Deployment (CI/CD) workflows are determined by organization cultures and preferences as well as technical requirements.
-* Does not provide application-level services, such as middleware (for example, message buses), data-processing frameworks (for example, Spark), databases (for example, mysql), caches, nor cluster storage systems (for example, Ceph) as built-in services. Such components can run on Kubernetes, and/or can be accessed by applications running on Kubernetes through portable mechanisms, such as the Open Service Broker.
+* Does not provide application-level services, such as middleware (for example, message buses), data-processing frameworks (for example, Spark), databases (for example, mysql), caches, nor cluster storage systems (for example, Ceph) as built-in services. Such components can run on Kubernetes, and/or can be accessed by applications running on Kubernetes through portable mechanisms, such as the [Open Service Broker](https://openservicebrokerapi.org/).
 * Does not dictate logging, monitoring, or alerting solutions. It provides some integrations as proof of concept, and mechanisms to collect and export metrics.
 * Does not provide nor mandate a configuration language/system (for example, jsonnet). It provides a declarative API that may be targeted by arbitrary forms of declarative specifications.
 * Does not provide nor adopt any comprehensive machine configuration, maintenance, management, or self-healing systems.