add spoiler surrounding topics

.gitea/issue_template/proposal.yaml

@@ -14,6 +14,17 @@ body:
       placeholder: stofl, inspired by https://codeforces.com/problemset/problem/1/A
     validations:
       required: true
+  - type: textarea
+    id: spoiler-begin
+    attributes:
+      label: Start of spoiler
+      description: Opening the spoiler tag
+      placeholder: |
+        <details>
+        <summary>Topic Tags</summary>
+      value: |
+        <details>
+        <summary>Topic Tags</summary>
   - type: dropdown
     id: round
     attributes:
@@ -110,6 +121,13 @@ body:
         - warmup
     validations:
       required: false
+  - type: textarea
+    id: spoiler-end
+    attributes:
+      label: End of spoiler
+      description: Closing the spoiler tag
+      placeholder: </details>
+      value: </details>
   - type: markdown
     attributes:
       value: |