docs: fix links (#255)

docs/crd_v1alpha1.md

@@ -1,11 +1,11 @@
 # FlinkCluster Custom Resource Definition - v1alpha1
 
-The Kubernetes Operator for Apache Flink uses  [CustomResourceDefinition](https://kubernetes.io/docs/concepts/api-extension/custom-resources/)
+The Kubernetes Operator for Apache Flink uses [CustomResourceDefinition](https://kubernetes.io/docs/concepts/api-extension/custom-resources/)
 named `FlinkCluster` for specifying a Flink job cluster ([sample](../config/samples/flinkoperator_v1beta1_flinkjobcluster.yaml))
 or Flink session cluster ([sample](../config/samples/flinkoperator_v1beta1_flinksessioncluster.yaml)), depending on
 whether the job spec is specified. Similarly to other kinds of Kubernetes resources, the custom resource consists of a
 resource `Metadata`, a specification in a `Spec` field and a `Status` field. The definitions are organized in the
-following structure. The v1beta1 version of the API definition is implemented [here](../api/v1beta1/flinkcluster_types.go).
+following structure. The v1beta1 version of the API definition is implemented [here](../apis/flinkcluster/v1beta1/flinkcluster_types.go).
 
 ```
 FlinkCluster

docs/developer_guide.md

@@ -8,7 +8,7 @@ library. The project structure and boilerplate files are generated with
 [Kubebuilder](https://github.com/kubernetes-sigs/kubebuilder). Knowledge of
 controller-runtime and Kubebuilder is required to understand this project.
 
-The Flink custom resource is defined in Go struct [FlinkCluster](../api/v1beta1/flinkcluster_types.go),
+The Flink custom resource is defined in Go struct [FlinkCluster](../apis/flinkcluster/v1beta1/flinkcluster_types.go),
 then Kubebuild generates related Go files and YAML files, e.g.
 [flinkclusters.yaml](../config/crd/bases/flinkoperator.k8s.io_flinkclusters.yaml).
 The custom logic for reconciling a Flink custom resource is inside of the