ECOM-632 added asterix explanation footnote

lms/static/sass/views/_login-register.scss

@@ -95,6 +95,13 @@
         }
     }
 
+    .note {
+        @extend %t-copy-sub2;
+        display: block;
+        font-weight: normal;
+        color: $gray;
+        margin-top: 15px;
+    }
 
 
     /** The forms **/

lms/templates/student_account/register.underscore

@@ -25,4 +25,6 @@
     <%= context.fields %>
 
     <button class="action action-primary action-update js-register register-button"><%- gettext("Register") %></button>
+
+    <p class="note">* <%- gettext("Required fields") %></p>
 </form>