Add the links to the tutorial pages

src/pages/LandingPage.svelte

@@ -2,10 +2,9 @@
   import "../style/main.css";
   // @ts-expect-error no declarations
   import { initAll } from "govuk-frontend";
-  import { DefaultButton } from "govuk-svelte";
+  import { DefaultButton, SecondaryButton } from "govuk-svelte";
   import About from "lib/common/About.svelte";
-  import { SecondaryButton } from "govuk-svelte";
-  import { Beta, Header } from "lib/common";
+  import { Beta, ExternalLink, Header } from "lib/common";
   import { onMount } from "svelte";
 
   let showAbout = false;
@@ -38,6 +37,13 @@
     files that can be shared with others using this tool or imported into other
     GIS software.
   </p>
+  <h3>Tutorial</h3>
+  <p>
+    <ExternalLink href="https://www.youtube.com/watch?v=6u2lK8xzQfM">
+      Here
+    </ExternalLink> is a tutorial explaining the use of the scheme sketcher for all
+    users, including guidance at those submitting sketches for ATE review.
+  </p>
   <DefaultButton on:click={goToSketcher}>Start</DefaultButton>
 
   <h2>Browse existing sketches and geographic context:</h2>

src/pages/SketchSchemes.svelte

@@ -29,6 +29,7 @@
   import { writable } from "svelte/store";
   import { emptySchemes } from "scheme-sketcher-lib/draw/stores";
   import { getKey } from "lib/common/files";
+    import ExternalLink from "lib/common/ExternalLink.svelte";
 
   // FileManagement will set this up
   let gjSchemes = writable(emptySchemes(cfg));
@@ -90,6 +91,7 @@
       </div>
 
       <h2 style="margin-bottom: 0px">Scheme Sketcher</h2>
+      <ExternalLink href="https://www.youtube.com/watch?v=6u2lK8xzQfM">Tutorial</ExternalLink>
     {/if}
 
     <FileManagement {gjSchemes} {authority} {filename} />