fix(examples): add token counting example

examples/count-tokens.ts

@@ -0,0 +1,20 @@
+#!/usr/bin/env -S npm run tsn -T
+
+import Anthropic from '@anthropic-ai/sdk';
+
+const client = new Anthropic(); // gets API Key from environment variable ANTHROPIC_API_KEY
+
+async function main() {
+  const result = await client.messages.countTokens({
+    messages: [
+      {
+        role: 'user',
+        content: 'Hey Claude!?',
+      },
+    ],
+    model: 'claude-3-5-sonnet-latest',
+  });
+  console.dir(result);
+}
+
+main();