docs: rename .readme_partials to .readme-partials (#48)

* docs: rename .readme-partials to .readme-partials * add quotes

Author: anguillanneuf

.readme_partials.yaml .readme-partials.yaml.readme_partials.yaml renamed to .readme-partials.yaml

@@ -1,6 +1,6 @@
 custom_content: |
  #### Publishing messages
- With Pub/Sub Lite, you can use a Producer<byte[], byte[]> to publish messages:
+ With Pub/Sub Lite, you can use a `Producer<byte[], byte[]>` to publish messages:
  ```java
  import com.google.cloud.pubsublite.kafka.ProducerSettings;
  import org.apache.kafka.clients.producer.*;