Add a placeholder text in the comment form to invite the user to be polite.

Author: Julien Jorge

app/views/comments/_form.html.haml

@@ -5,7 +5,7 @@
   = form.text_field :title, autocomplete: 'off', required: 'required', spellcheck: 'true', maxlength: 100
 %p
   = form.label :wiki_body, "Commentaire complet"
-  = form.text_area :wiki_body, required: 'required', spellcheck: 'true', class: 'markItUp'
+  = form.text_area :wiki_body, required: 'required', spellcheck: 'true', class: 'markItUp', placeholder: "Vous pouvez écrire votre commentaire ici.\n\nMerci de rester poli et courtois, on compte sur vous !"
 %p
   = form.submit "Prévisualiser", id: "comment_preview"
   = form.submit "Poster le commentaire", 'data-disable-with' => "Enregistrement en cours" if @preview_mode