Hide documentation link for unofficial themes (fix #2076), add OsmCha link

src/UI/BigComponents/AboutMapComplete.svelte

@@ -16,6 +16,7 @@
   import Bug from "../../assets/svg/Bug.svelte"
   import ThemeViewState from "../../Models/ThemeViewState"
   import DocumentChartBar from "@babeard/svelte-heroicons/outline/DocumentChartBar"
+  import DocumentMagnifyingGlass from "@babeard/svelte-heroicons/outline/DocumentMagnifyingGlass"
 
   export let state: ThemeViewState
 
@@ -48,12 +49,13 @@
     <Tr t={Translations.t.general.attribution.openIssueTracker} />
   </a>
 
+  {#if layout.official}
     <a
       class="flex"
       href={"https://github.com/pietervdvn/MapComplete/blob/develop/Docs/Themes/" + layout.id + ".md"}
       target="_blank"
     >
-    <DocumentChartBar class="h-6 w-6" />
+      <DocumentMagnifyingGlass class="h-6 w-6" />
       <Tr
         t={Translations.t.general.attribution.openThemeDocumentation.Subs({
           name: layout.title,
@@ -61,6 +63,12 @@
       />
     </a>
 
+    <a class="flex" href={Utils.OsmChaLinkFor(31, layout.id)}>
+      <DocumentChartBar class="h-6 w-6" />
+      <Tr t={Translations.t.general.attribution.openOsmcha.Subs({theme: layout.title})}/>
+    </a>
+  {/if}
+
   <a class="flex" href="https://en.osm.town/@MapComplete" target="_blank">
     <Mastodon class="h-6 w-6" />
     <Tr t={Translations.t.general.attribution.followOnMastodon} />