Add income hint text

app/models/form/sales/questions/buyer1_income.rb

@@ -4,6 +4,7 @@ class Form::Sales::Questions::Buyer1Income < ::Form::Question
     @id = "income1"
     @check_answer_label = "Buyer 1’s gross annual income"
     @header = "Buyer 1’s gross annual income"
+    @hint_text = "Provide the gross annual income (i.e. salary before tax) plus the annual amount of benefits, Universal Credit or pensions, and income from investments."
     @type = "numeric"
     @min = 0
     @max = 999_999

app/models/form/sales/questions/buyer2_income.rb

@@ -5,6 +5,7 @@ class Form::Sales::Questions::Buyer2Income < ::Form::Question
     @check_answer_label = "Buyer 2’s gross annual income"
     @header = "Buyer 2’s gross annual income"
     @type = "numeric"
+    @hint_text = "Provide the gross annual income (i.e. salary before tax) plus the annual amount of benefits, Universal Credit or pensions, and income from investments."
     @min = 0
     @step = 1
     @width = 5

spec/models/form/sales/questions/buyer1_income_spec.rb

@@ -32,7 +32,7 @@ RSpec.describe Form::Sales::Questions::Buyer1Income, type: :model do
   end
 
   it "has the correct hint" do
-    expect(question.hint_text).to be_nil
+    expect(question.hint_text).to eq("Provide the gross annual income (i.e. salary before tax) plus the annual amount of benefits, Universal Credit or pensions, and income from investments.")
   end
 
   it "has correct width" do

spec/models/form/sales/questions/buyer2_income_spec.rb

@@ -32,7 +32,7 @@ RSpec.describe Form::Sales::Questions::Buyer2Income, type: :model do
   end
 
   it "has the correct hint" do
-    expect(question.hint_text).to be_nil
+    expect(question.hint_text).to eq("Provide the gross annual income (i.e. salary before tax) plus the annual amount of benefits, Universal Credit or pensions, and income from investments.")
   end
 
   it "has correct width" do