Add puzzle fake data recommendation

app/views/puzzles/_form.html.slim

@@ -1,4 +1,7 @@
 = form_with model: puzzle, url: url, method: method do |form|
+  .row.mb-3
+    .col.alert.alert-warning
+      = t("puzzles.form.fake_data_recommendation")
   .row.mb-3
     .col
       .form-floating

config/locales/en.yml

@@ -143,6 +143,8 @@ en:
   puzzles:
     edit:
       title: "Edit contest puzzle"
+    form:
+      fake_data_recommendation: It is recommended to first enter a fake name and image, and to use the real ones only once the contest starts.
     image_select: "Select an image"
     new:
       title: "New contest puzzle"

config/locales/fr.yml

@@ -114,6 +114,8 @@ fr:
   puzzles:
     edit:
       title: "Modifier le puzzle"
+    form:
+      fake_data_recommendation: Il est recommendé d'entrer de faux noms et images, et de mettre les vrais uniquement quand le concours démarre.
     image_select: "Choisis une image"
     new:
       title: "Nouveau puzzle"