Update actors_api.md (#414)

reference/api/actors_api.md

@@ -8,6 +8,7 @@ Besides the language specific Dapr SDKs, a developer can invoke an actor using t
 - [Service Code Calling to Dapr](#specifications-for-user-service-code-calling-to-dapr)
   - [Invoke Actor Method](#invoke-actor-method)
   - [Save Actor State](#save-actor-state)
+  - [Delete Actor State](#delete-actor-state)
   - [Actor State Transactions](#actor-state-transactions)
   - [Get Actor State](#get-actor-state)
   - [Create Actor Reminder](#create-actor-reminder)
@@ -81,6 +82,33 @@ curl -X POST http://localhost:3500/v1.0/actors/x-wing/33/method/fly \
 ```
 The response (the method return) from the remote endpoint is returned in the request body.
 
+### Delete actor state
+
+Deletes the state key of an actor
+
+#### HTTP Request
+
+```http
+DELETE http://localhost:<daprPort>/v1.0/actors/<actorType>/<actorId>/state/<key>
+```
+
+#### HTTP Response Codes
+
+Code | Description
+---- | -----------
+200  | Request successful
+500  | Request failed
+404  | Actor not found
+
+#### URL Parameters
+
+Parameter | Description
+--------- | -----------
+daprPort | The Dapr port.
+actorType | The actor type.
+actorId | The actor ID.
+key | the key of the state to delete
+
 ### Save actor state
 
 Persists the changed to the state for an actor