Update Readme, converter helper script can now reads straight from http

Readme.md

@@ -118,6 +118,16 @@ in a local folder - for example schemas. Then we specify this folder as an addit
 $ ./bin/kubeconform -registry kubernetesjsonschema.dev -registry 'schemas/{{ .ResourceKind }}{{ .KindSuffix }}.json' fixtures/custom-resource.yaml
 ```
 
+### Generating a JSON schema from an OpenAPI file
+
+Kubeconform uses JSON schemas to validate Kubernetes resources. For Custom Resource, the CustomResourceDefinition
+first needs to be converted to JSON Schema. A script is provided to convert these CustomResourceDefinitions 
+to JSON schema. Here is an example how to use it:
+
+```
+$ ./cmd/openapi2jsonschema/main.py https://raw.githubusercontent.com/aws/amazon-sagemaker-operator-for-k8s/master/config/crd/bases/sagemaker.aws.amazon.com_trainingjobs.yaml > fixtures/registry/trainingjob-sagemaker-v1.json
+```
+
 ### Credits
 
  * @garethr for the [Kubeval](https://github.com/instrumenta/kubeval) and

cmd/openapi2jsonschema/main.py

@@ -4,6 +4,7 @@
 import yaml
 import json
 import sys
+import urllib.request
 
 def iteritems(d):
     if hasattr(dict, "iteritems"):
@@ -90,7 +91,11 @@ if len(sys.argv) == 0:
     print("missing file")
     exit(1)
 
-with open(sys.argv[1]) as f:
+if sys.argv[1].startswith("http"):
+  f = urllib.request.urlopen(sys.argv[1])
+else:
+  f = open(sys.argv[1])
+with f:
     y = yaml.load(f, Loader=yaml.SafeLoader)
     schema = y["spec"]["validation"]["openAPIV3Schema"]
     schema = additional_properties(schema)