Clarify playground executes in browser (#38)

Author: lucacasonato

about.md

@@ -14,11 +14,16 @@ This website was originally developed and designed by Luca Casonato.
 Many thanks to Tim Chevalier for his work on a large part of the documentation
 content.
 
+The MessageFormat logo was designed by Luca Casonato.
+
+## Playground
+
 The playground and interactive code blocks format messages using the JavaScript
 implementation of MessageFormat 2, maintained by Eemeli Aro. Highlighting and
 other language features are powered by the
 [MessageFormat 2 Language Server](https://github.com/lucacasonato/mf2-tools),
 maintained by Luca Casonato and Nicolò Ribaudo.
 
-
-The MessageFormat logo was designed by Luca Casonato.
+All validation and formatting of messages happens in your browser using the JS
+implementation and the language server (via WASM). No data is sent to any
+server.

playground.tsx

@@ -188,6 +188,15 @@ export default function IndexPage({ comp }: any) {
                 quick start guide
               </a>.
             </p>
+            <p class="text-black">
+              The playground{" "}
+              <a
+                href="/about/#playground"
+                class="text-blue-700 underline"
+              >
+                validates and formats messages in your browser
+              </a>. The message or data you enter is not sent to any server. .
+            </p>
           </div>
           <div class="px-2 space-y-2">
             <h2 class="text-xl font-bold font-serif pb-1 text-black">