show max topics limit in heroku kafka:info

some clusters have a max number of topics. If there is one, display it
in the CLI output like so:

```
Topics:    0 / 10 topics, see heroku kafka:topics
```

commands/info.js

@@ -29,10 +29,17 @@ function formatInfo (info) {
 
   // we hide __consumer_offsets in topic listing; don't count it
   const topicCount = cluster.topics.filter((topic) => topic !== '__consumer_offsets').length
-  lines.push({
-    name: 'Topics',
-    values: [`${topicCount} ${humanize.pluralize(topicCount, 'topic')}, see heroku kafka:topics`]
-  })
+  if (cluster.limits && cluster.limits.max_topics) {
+    lines.push({
+      name: 'Topics',
+      values: [`${topicCount} / ${cluster.limits.max_topics} ${humanize.pluralize(topicCount, 'topic')}, see heroku kafka:topics`]
+    })
+  } else {
+    lines.push({
+      name: 'Topics',
+      values: [`${topicCount} ${humanize.pluralize(topicCount, 'topic')}, see heroku kafka:topics`]
+    })
+  }
 
   if (cluster.topic_prefix) {
     lines.push({ name: 'Prefix', values: [cluster.topic_prefix] })