[skip ci]Add an automerge rule for document changes (#5005)

Signed-off-by: NXiangyu Wang <xiangyu.wang@zilliz.com>

.github/mergify.yml

@@ -22,3 +22,15 @@ pull_request_rules:
       merge:
         method: squash
 
+  - name: automatic merge for master when document files changed only and the title does not contain “[WIP]”
+    conditions:
+      - base=master
+      - -title~=(?i)\[wip\]
+      - "label=PR | automerge"
+      - "#approved-reviews-by>=1"
+      - "#changes-requested-reviews-by=0"
+      - "status-success=DCO"
+      - -files~=\.(?!md|png)
+    actions:
+      merge:
+        method: squash