Docs: Update changelog and docs for annotation region change (#18593)

CHANGELOG.md

@@ -1,5 +1,10 @@
 # 6.4.0 (unreleased)
 
+### Breaking changes
+
+* **Annotations**: There are some breaking changes in the annotations HTTP API for region annotations. Region
+    annotations are now represented using a single event instead of two seperate events. Check HTTP docs for more details.
+
 # 6.3.3 (2019-08-15)
 
 ### Bug Fixes

docs/sources/http_api/annotations.md

@@ -27,7 +27,6 @@ Content-Type: application/json
 Authorization: Basic YWRtaW46YWRtaW4=
 ```
 
-
 Query Parameters:
 
 - `from`: epoch datetime in milliseconds. Optional.
@@ -88,9 +87,13 @@ Content-Type: application/json
 
 **Example Request**:
 
+```http
+POST /api/annotations/graphite HTTP/1.1
 Accept: application/json
 Content-Type: application/json
-HTTP/1.1 200
+
+```
+
 **Example Response**:
 
 ```http
@@ -120,10 +123,13 @@ Content-Type: application/json
 ```http
 HTTP/1.1 200
 Content-Type: application/json
-> This is available in Grafana 6.0.0-beta2 and above.
 
 ```
 
+## Patch Annotation
+> This is available in Grafana 6.0.0-beta2 and above.
+
+`PATCH /api/annotations/:id`
 
 Updates one or more properties of an annotation that matches the specified id.
 
@@ -198,7 +204,7 @@ Content-Type: application/json
 
 Updates one or more properties of an annotation that matches the specified id.
 
-This operation currently supports updating of the `text`, `tags`, `time` and `timeEnd` properties. 
+This operation currently supports updating of the `text`, `tags`, `time` and `timeEnd` properties.
 
 **Example Request**:
 
@@ -249,4 +255,4 @@ Content-Type: application/json
 {
     "message":"Annotation deleted"
 }
-```
+```