Add mortgage length hint (#1237)

app/models/form/sales/questions/mortgage_length.rb

@@ -8,5 +8,6 @@ class Form::Sales::Questions::MortgageLength < ::Form::Question
     @min = 0
     @width = 5
     @suffix = " years"
+    @hint_text = "You should round up to the nearest year. Value should not exceed 60 years."
   end
 end

spec/models/form/sales/questions/mortgage_length_spec.rb

@@ -32,7 +32,9 @@ RSpec.describe Form::Sales::Questions::MortgageLength, type: :model do
   end
 
   it "has the correct hint" do
-    expect(question.hint_text).to be_nil
+    expect(question.hint_text).to eq(
+      "You should round up to the nearest year. Value should not exceed 60 years.",
+    )
   end
 
   it "has correct width" do