🐛Add parent blurb to signup birthdate check

app/locale/en.coffee

@@ -304,6 +304,7 @@
     signup_as_individual: "Sign up as an Individual"
     enter_class_code: "Enter your Class Code"
     enter_birthdate: "Enter your birthdate:"
+    parent_use_birthdate: "Parents, use your own birthdate."
     ask_teacher_1: "Ask your teacher for your Class Code."
     ask_teacher_2: "Not part of a class? Create an "
     ask_teacher_3: "Individual Account"

app/styles/modal/create-account-modal/segment-check-view.sass

@@ -16,3 +16,7 @@
   
   .teacher-name
     font-size: 14pt
+
+  .parent_birthdate
+    font-size: 11pt
+    margin-top: 20px

app/templates/core/create-account-modal/segment-check-view.jade

@@ -50,6 +50,7 @@ form.modal-body.segment-check
               - var thisYear = new Date().getFullYear()
               for year in _.range(thisYear, thisYear - 100, -1)
                 option(selected=(year == view.signupState.get('birthdayYear'))) #{year}
+        .parent_birthdate(data-i18n="signup.parent_use_birthdate")
 
       default
         p