Added required external components

docs/modules/druid/pages/required-external-components.adoc

@@ -0,0 +1,9 @@
+# Required external components
+
+Druid uses an SQL database to store metadata. Consult the https://druid.apache.org/docs/latest/dependencies/metadata-storage.html#available-metadata-stores[Druid documentation] for a list of supported databases and setup instructions.
+
+## Feature specific: S3 and cloud deep storage
+
+https://druid.apache.org/docs/latest/dependencies/deep-storage.html[Deep storage] is where segments are stored. Druid offers multiple storage backends. For the local storage there are no prerequisites. HDFS deep storage can be set up with the xref:hdfs:index.adoc[Stackable Operator for Apache HDFS]. For S3 deep storage or the Google Cloud and Azure storage backends, you need to set up the storage.
+
+Read the xref:usage-guide/deep-storage.adoc[deep storage usage guide] to learn more about configuring Druid deep storage.

docs/modules/druid/pages/usage-guide/deep-storage.adoc

@@ -1,8 +1,10 @@
 = Deep storage configuration
 
+https://druid.apache.org/docs/latest/dependencies/deep-storage.html[Deep Storage] is where Druid stores data segments. For a Kubernetes environment, either the HDFS or S3 backend is recommended.
+
 == [[hdfs]]HDFS
 
-Druid can use HDFS as a backend for deep storage:
+Druid can use HDFS as a backend for deep storage, which requires having an HDFS instance running. You can use the xref:hdfs:index.adoc[Stackable Operator for Apache HDFS] to run HDFS. Configure the HDFS deep storage backend in your Druid cluster this way:
 
 [source,yaml]
 ----
@@ -80,4 +82,4 @@ include::partial$s3-note.adoc[]
 
 === S3 Credentials
 
-include::partial$s3-credentials.adoc[]
+include::partial$s3-credentials.adoc[]