Add an error page

Fixes #3.

emojos.py

@@ -33,7 +33,7 @@ def emojo(domain):
                        key=operator.itemgetter('shortcode'))
         return render_template('emojo.html', domain=domain, emojo=emojo)
     except requests.exceptions.RequestException as e:
-        return render_template('oh_no.html')
+        return render_template('oh_no.html', domain=domain)
 
 
 @app.route('/favicon.ico')

templates/oh_no.html

@@ -0,0 +1,5 @@
+{% extends "base.html" %}
+{% block title %}Custom emoji list for {{ domain }}{% endblock title %}
+{% block body %}
+<p><b>{{ domain }}</b> isn't a fediverse instance or doesn't have a <code>v1/custom_emojis</code> endpoint. :(</p>
+{% endblock body %}