friendlier content warning placeholder

Author: marylychee

lib/depject/message/html/compose.js

@@ -72,7 +72,7 @@ exports.create = function (api) {
     })
 
     const contentWarningInput = h('input.contentWarning', {
-      placeholder: 'content warning (optional)',
+      placeholder: 'Write a content warning (optional)',
       'ev-input': function () {
         refreshHasContent()
         queueSave()