re-add max-w-prose to /primary-docs (#482)

Author: Fbasham

Diff for: frontend/app/routes/protected/sin-application/primary-docs-form.tsx

@@ -48,7 +48,7 @@ export default function PrimaryDocsForm({
   }
 
   return (
-    <div className="space-y-6">
+    <div className="max-w-prose space-y-6">
       <CurrentStatusInCanada
         value={currentStatus}
         onChange={handleOnCurrentStatusInCanadaChanged}