Add Nextclade section on Splash

Now that sections aren't required to have preview cards, a section for
Nextclade without any cards can visually fit in.

static-site/src/components/splash/index.jsx

@@ -110,6 +110,13 @@ const Splash = () => {
           buttonText="Find out more"
           buttonLink="https://docs.nextstrain.org/en/latest/guides/communicate/narratives-intro.html"
         />
+        <Section
+          id="nextclade"
+          title="Nextclade"
+          abstract="Nextclade allows you to analyze virus genome sequences in the web browser. It will align your sequence data to a reference genome, call mutations relative to that reference, and place your sequences on a phylogeny. It also reports clade assignments and quality of your sequence data."
+          buttonText="Go to Nextclade"
+          buttonLink="https://clades.nextstrain.org"
+        />
       </div>
 
       <HugeSpacer/>