Add patient search help text (#148)

A reminder to use the details registered at the GP.

![Screenshot 2025-01-09 at 14 43
13](https://github.com/user-attachments/assets/47dbd496-ee02-4611-964b-4c77d98c1eed)

Author: frankieroberto

app/views/vaccinate/patient-search.html

@@ -23,6 +23,8 @@
 
       <h1 class="nhsuk-heading-l">Search for the patient</h1>
 
+      <p class="nhsuk-body">Make sure the details you enter match those registered with the patient’s GP.</p>
+
       <form action="/vaccinate/patient-search" method="post">
         {{ input({
           label: {