Added exercise 18.1 solution

Author: 0mppula

18_http_and_forms/content_negotiation.js

@@ -0,0 +1,11 @@
+const url = 'https://eloquentjavascript.net/author';
+const types = ['text/plain', 'text/html', 'application/json', 'application/rainbows+unicorns'];
+
+async function showTypes() {
+	for (let type of types) {
+		let resp = await fetch(url, { headers: { accept: type } });
+		console.log(`${type}: ${await resp.text()}\n`);
+	}
+}
+
+showTypes();