Rename exercises dir

Name it instead "topics" so it won't be
strange if some topics included "exercises" directory.

topics/kafka/README.md

@@ -0,0 +1,46 @@
+# Apache Kafka
+
+## Kafka Exercises
+
+|Name|Topic|Objective & Instructions|Solution|Comments|
+|--------|--------|------|----|----|
+
+## Kafka Self Assessment
+
+* [Kafka 101](#questions-kafka-101)
+
+<a name="questions-kafka-101"></a>
+### Kafka 101
+
+<details>
+<summary>What is Kafka?</summary><br><b>
+
+[kafka.apache.org](https://kafka.apache.org): "Apache Kafka is an open-source distributed event streaming platform used by thousands of companies for high-performance data pipelines, streaming analytics, data integration, and mission-critical applications."
+
+In other words, Kafka is a sort of distributed log where you can store events, read them and distribute them to different services and do it in high-scale and real-time.
+</b></details>
+
+<details>
+<summary>What Kafka is used for?</summary><br><b>
+
+- Real-time e-commerce
+- Banking
+- Health Care
+- Automotive (traffic alerts, hazard alerts, ...)
+- Real-time Fraud Detection
+</b></details>
+
+<details>
+<summary>What is a "Producer" in regards to Kafka?</summary><br><b>
+
+An application that publishes data to the Kafka cluster.
+</b></details>
+
+<a name="questions-kafka-architecture"></a>
+### Kafka Architecture
+
+<details>
+<summary>What's in a Kafka cluster?</summary><br><b>
+
+- Broker: a server with kafka process running on it. Such server has local storage. In a single Kafka clusters there are usually multiple brokers.
+</b></details>