Address review comments

docs/sources/http_api/annotations.md

@@ -189,6 +189,8 @@ Content-Type: application/json
 
 Updates one or more properties of an annotation that matches the specified id.
 
+The `PATCH` operation currently supports updating of the `text`, `tags`, `time` and `timeEnd` properties. It does not handle updating of the `isRegion` and `regionId` properties. To make an annotation regional or vice versa, consider using the `PUT` operation.
+
 **Example Request**:
 
 ```json
@@ -198,8 +200,6 @@ Authorization: Bearer eyJrIjoiT0tTcG1pUlY2RnVKZTFVaDFsNFZXdE9ZWmNrMkZYbk
 Content-Type: application/json
 
 {
-  "time":1507037197000,
-  "timeEnd":1507180807095,
   "text":"New Annotation Description",
   "tags":["tag6","tag7","tag8"]
 }

pkg/api/annotations.go

@@ -222,7 +222,7 @@ func PatchAnnotation(c *m.ReqContext, cmd dtos.PatchAnnotationsCmd) Response {
 	items, err := repo.Find(&annotations.ItemQuery{AnnotationId: annotationID, OrgId: c.OrgId})
 
 	if err != nil || len(items) == 0 {
-		return Error(500, "Could not find annotation to update", err)
+		return Error(404, "Could not find annotation to update", err)
 	}
 
 	existing := annotations.Item{