opensearch: Add automatic manifest updates

https://developer.mozilla.org/en-US/docs/Web/XML/Guides/OpenSearch#supporting_automatic_updates_for_opensearch_description

Author: fstachura

static/search.xml

@@ -6,4 +6,5 @@
   <Image width="16" height="16" type="image/x-icon">https://elixir.bootlin.com/favicon.ico</Image>
   <Url rel="results" type="text/html" template="https://elixir.bootlin.com/linux/latest/A/ident/{searchTerms}"/>
   <Url rel="suggestions" type="application/x-suggestions+json" template="https://elixir.bootlin.com/acp?q={searchTerms}&amp;f=A&amp;p=linux&amp;opensearch=true"/>
+  <Url type="application/opensearchdescription+xml" rel="self" template="https://elixir.bootlin.com/static/search.xml" />
 </OpenSearchDescription>