Add serving doc

docs/serving.md

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+# Serving Predictions
+
+Depending on whether you deployed Seldon Core with Ambassador or the API Gateway you can access your models as discussed below:
+
+# Ambassador
+
+## Ambassador REST
+
+Assuming Ambassador is exposed at ```<ambassadorEndpoint>``` and with a Seldon deployment name ```<deploymentName>```:
+
+ * A REST endpoint will be exposed at : ```http://<ambassadorEndpoint>/seldon/<deploymentName>/api/v0.1/predictions```
+
+
+## Ambassador gRPC
+
+Assuming Ambassador is exposed at ```<ambassadorEndpoint>``` and with a Seldon deployment name ```<deploymentName>```:
+
+  * A gRPC endpoint will be exposed at ```<ambassadorEndpoint>``` and you should send metadata in your request with key ```seldon``` and value ```<deploymentName>```.
+
+
+# API OAuth Gateway
+
+The HTTP and OAuth endpoints will be on separate ports, default is 8080 (HTTP) and 5000 (gRPC).
+
+## OAuth REST
+
+Assuming the API Gateway is exposed at ```<APIGatewayEndpoint>```
+
+ 1. You should get an OAuth token from ```<APIGatewayEndpoint>/oauth/token```
+ 1. You should make prediction requests to ```<APIGatewayEndpoint>/api/v0.1/predictions``` with the OAuth token in the header as ```Authorization: Bearer <token>```
+
+## OAuth gRPC
+
+Assuming the API gRPC Gateway is exposed at ```<APIGatewayEndpoint>```
+
+ 1. You should get an OAuth token from ```<APIGatewayEndpoint>/oauth/token```
+ 1. Send gRPC requests to ```<APIGatewayEndpoint>``` with the OAuth token in the meta data as ```oauth_token: <token>```
+
+# Client Implementations
+
+## Curl Examples
+
+### Ambassador REST
+
+Assuming a SeldonDeplotment ```mymodel``` with Ambassador exposed on 0.0.0.0:8003:
+
+```
+curl -v 0.0.0.0:8003/seldon/mymodel/api/v0.1/predictions -d '{"data":{"names":["a","b"],"tensor":{"shape":[2,2],"values":[0,0,1,1]}}}' -H "Content-Type: application/json"
+```
+
+
+### API OAuth Gateway REST
+
+Assume server is accessible at 0.0.0.0:8002.
+
+Get a token. Assuming the OAuth key is ```oauth-key``` and OAuth secret is ```oauth-secret``` as specified in the SeldonDeployment graph you created:
+
+```
+TOKENJSON=$(curl -XPOST -u oauth-key:oauth-secret 0.0.0.0:8002/oauth/token -d 'grant_type=client_credentials')
+TOKEN=$(echo $TOKENJSON | jq ".access_token" -r)
+```
+
+Get predictions
+```
+curl -w "%{http_code}\n" --header "Authorization: Bearer $TOKEN" 0.0.0.0:8002/api/v0.1/predictions -d '{"data":{"names":["a","b"],"tensor":{"shape":[2,2],"values":[0,0,1,1]}}}' -H "Content-Type: application/json"
+```
+
+## OpenAPI REST
+
+Use Swagger to generate a client for you from the [OpenAPI specifications](../openapi/README.md).
+
+## gRPC
+
+Use [gRPC](https://grpc.io/) tools in your desired language from the [proto buffer specifications](../proto/prediction.proto).
+
+### Example Python
+
+See [example python code](../notebooks/seldon_utils.py).
+