Additional translatable line for blurb placeholder

A new commit to replace https://github.com/HabitRPG/habitrpg/pull/5293
which turned messy after I rebased accidentally

New screenshot: http://i.snag.gy/m9gTA.jpg

common/locales/en/character.json

@@ -140,5 +140,6 @@
     "unequipBattleGear": "Unequip Battle Gear",
     "unequipCostume": "Unequip Costume",
     "unequipPetMountBackground": "Unequip Pet, Mount, Background",
-    "animalSkins": "Animal Skins"
+    "animalSkins": "Animal Skins",
+    "displayBlurbPlaceholder": "Please introduce yourself"
 }

website/views/options/profile.jade

@@ -270,7 +270,7 @@ script(id='partials/options.profile.profile.html', type='text/ng-template')
           input.form-control(type='url', ng-model='editingProfile.imageUrl', placeholder=env.t('imageUrl'))
         .form-group
           label=env.t('displayBlurb')
-          textarea.form-control(rows=5, placeholder=env.t('displayBlurb'), ng-model='editingProfile.blurb')
+          textarea.form-control(rows=5, placeholder=env.t('displayBlurbPlaceholder'), ng-model='editingProfile.blurb')
           include ../shared/formatting-help
 
 mixin backgrounds(mobile)