doc(rest): add docs for rest api

docs/en_US/restapi/overview.md

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+Kuiper provides a set of REST API for streams and rules management in addition to CLI. 
+
+By default, the REST API are running in port 8080. You can change the port in `/etc/kuiper.yaml` for the `restPort` property.
+
+- [Streams](streams.md)
+- [Rules](rules.md)
+

docs/en_US/restapi/rules.md

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+# Rules management
+
+The Kuiper REST api for rules allows you to manage rules, such as create, show, drop, describe, start, stop and restart rules. 
+
+## create a rule
+
+The API accepts a JSON content and create and start a rule.
+```shell
+POST http://localhost:8080/rules
+```
+Request Sample
+
+```json
+{
+  "id": "rule1",
+  "sql": "SELECT * FROM demo",
+  "actions": [{
+    "log":  {}
+  }]
+}
+```
+
+
+## show rules
+
+The API is used for displaying all of rules defined in the server.
+
+```shell
+GET http://localhost:8080/rules
+```
+
+Response Sample:
+
+```json
+["rule1","rule2"]
+```
+
+## describe a rule
+
+The API is used for print the detailed definition of rule.
+
+```shell
+GET http://localhost:8080/rules/{id}
+```
+
+Path parameter `id` is the id or name of the rule.
+
+Response Sample: 
+
+```json
+{
+  "sql": "SELECT * from demo",
+  "actions": [
+    {
+      "log": {}
+    },
+    {
+      "mqtt": {
+        "server": "tcp://127.0.0.1:1883",
+        "topic": "demoSink"
+      }
+    }
+  ]
+}
+```
+
+## drop a rule
+
+The API is used for drop the rule.
+
+```shell
+DELETE http://localhost:8080/rules/{id}
+```
+
+
+## start a rule
+
+The API is used to start running the rule.
+
+```shell
+POST http://localhost:8080/rules/{id}/start
+```
+
+
+## stop a rule
+
+The API is used to stop running the rule.
+
+```shell
+POST http://localhost:8080/rules/{id}/stop
+```
+
+## restart a rule
+
+The API is used to restart the rule.
+
+```shell
+POST http://localhost:8080/rules/{id}/restart
+```
+
+## get the status of a rule
+
+The command is used to get the status of the rule. If the rule is running, the metrics will be retrieved realtime. The status can be
+- running with metrics: $metrics
+- stopped: $reason
+
+```shell
+GET http://localhost:8080/rules/{id}/status
+```
+
+Response Sample:
+
+```shell
+running with metrics:
+{
+    "source_demo_0_records_in_total":5,
+    "source_demo_0_records_out_total":5,
+    "source_demo_0_exceptions_total":0,
+    "source_demo_0_process_latency_ms":0,
+    "source_demo_0_buffer_length":0,
+    "source_demo_0_last_invocation":"2020-01-02T11:28:33.054821",
+    ... 
+    "op_filter_0_records_in_total":5,
+    "op_filter_0_records_out_total":2,
+    "op_filter_0_exceptions_total":0,
+    "op_filter_0_process_latency_ms":0,
+    "op_filter_0_buffer_length":0,
+    "op_filter_0_last_invocation":"2020-01-02T11:28:33.054821",
+    ...
+}
+```

docs/en_US/restapi/streams.md

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+# Streams management
+
+The Kuiper REST api for streams allows you to manage the streams, such as create, describe, show and drop stream definitions.
+
+## create a stream
+
+The API is used for creating a stream. For more detailed information of stream definition, please refer to [streams](../sqls/streams.md).
+
+```shell
+POST http://localhost:8080/rules
+```
+Request sample, the request is a json string with `sql` field.
+
+```json
+{"sql":"create stream my_stream (id bigint, name string, score float) WITH ( datasource = \"topic/temperature\", FORMAT = \"json\", KEY = \"id\")"}
+```
+
+This API can run any stream sql statements, not only stream creation.
+
+## show streams
+
+The API is used for displaying all of streams defined in the server.
+
+```shell
+GET http://localhost:8080/streams
+```
+
+Response Sample:
+
+```json
+["mystream"]
+```
+
+## describe a stream
+
+The API is used for print the detailed definition of stream.
+
+```shell
+GET http://localhost:8080/streams/{id}}
+```
+
+Response Sample:
+
+```shell
+{
+  "Name": "demo",
+  "StreamFields": [
+    {
+      "Name": "temperature",
+      "FieldType": {
+        "Type": 2
+      }
+    },
+    {
+      "Name": "ts",
+      "FieldType": {
+        "Type": 1
+      }
+    }
+  ],
+  "Options": {
+    "DATASOURCE": "demo",
+    "FORMAT": "JSON"
+  }
+}
+```
+
+## drop a stream
+
+The API is used for drop the stream definition.
+
+```shell
+DELETE http://localhost:8080/streams/{id}
+```