doc(www): document use of npx

Author: GochoMugo

www/index.html

@@ -200,6 +200,12 @@ <h2>Installation</h2>
                 You should now have program
                 <code class="language-bash">lw-client</code> available.
             </p>
+            <p>
+                You can also use
+                <code class="language-bash">npx local-webhooks</code> instead,
+                which executes <code class="language-bash">lw-client</code>
+                indirectly.
+            </p>
         </section>
 
         <section class="content">