workflow: add checkboxes for issue template

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -2,6 +2,15 @@ name: "Feature request"
 description: Feature request
 labels: ["enhancement: pending triage"]
 body:
+  - type: checkboxes
+    attributes:
+      label: Please make sure of the following things
+      description: You may select more than one, even select all.
+      options:
+        - label: I have read the [documentation](https://alist-doc.nn.ci).
+        - label: I'm sure there are no duplicate issues or discussions.
+        - label: I'm sure this feature is not implemented.
+        - label: I'm sure it's a reasonable and popular requirement.
   - type: textarea
     id: feature-description
     attributes: