Add guidance for adding custom licence HTML in footer

Author: stephencdaly

guide/content/components/footer.slim

@@ -51,6 +51,13 @@ p The footer provides copyright, licensing and other information about your
   code: footer_with_custom_copyright_and_licence,
   data: footer_copyright_and_licence_arguments)
 
+== render('/partials/example.*',
+  caption: "Footer with custom licence HTML",
+  code: footer_with_custom_licence_html) do
+
+  markdown:
+    The `meta_licence_html` slot allows replacing the licence information with any custom HTML.
+
 == render('/partials/example.*',
   caption: "Footer with navigation",
   code: footer_with_navigation)

guide/lib/examples/footer_helpers.rb

@@ -66,6 +66,16 @@ def footer_copyright_and_licence_arguments
       FOOTER_COPYRIGHT_AND_LICENCE
     end
 
+    def footer_with_custom_licence_html
+      <<~FOOTER
+        = govuk_footer do |footer|
+          - footer.with_meta_licence_html do
+            |> Some custom HTML for the licence,
+               perhaps with a
+            = govuk_footer_link_to("link", "https://x-govuk.github.io/")
+      FOOTER
+    end
+
     def footer_with_navigation
       <<~FOOTER_WITH_NAVIGATION
         = govuk_footer do |footer|