Add note about example context. See #245.

index.html

@@ -678,7 +678,7 @@ <h2>Contexts</h2>
 {
   <span class="highlight">"@context": [
     "https://w3.org/2018/credentials/v1",
-    ...
+    "https://example.com/examples/v1"
   ]</span>,
   "id": "http://dmv.example.gov/credentials/3732",
   "type": ["VerifiableCredential", "ProofOfAgeCredential"],
@@ -690,6 +690,21 @@ <h2>Contexts</h2>
 }
         </pre>
 
+        <p>
+The example above uses the base context
+(<code>https://w3.org/2018/credentials/v1</code>) to establish that the
+conversation is about a Verififiable Credential. It then adds an additional
+context (<code>https://example.com/examples/v1</code>) to establish that the
+conversation will also be about examples.
+        </p>
+
+        <p class="note">
+This document uses the Example Context
+(<code>https://example.com/examples/v1</code>) for the purposes of
+demonstrating examples. The Example Context MUST NOT be used for any other
+purpose such as in pilot or production systems.
+        </p>
+
         <p>
 The data available at <code>https://w3.org/2018/credentials/v1</code>
 is a static document that is never updated and MAY be downloaded and