Add details regarding watched namespaces for the DatadogMonitor objec…

…ts (#1158)

* Update datadog_monitor.md

What Does This PR Do?
- Adds additional context for use specifying the `namespaces`

Motivation:
https://datadog.zendesk.com/agent/tickets/1666229

* Update docs/datadog_monitor.md

Co-authored-by: Brett Blue <[email protected]>

* Update docs/datadog_monitor.md

Co-authored-by: Brett Blue <[email protected]>

* Update datadog_monitor.md

Updated of code block configuration for syntax corrections.

* Update datadog_monitor.md

Update of syntax of code block section for proper markup of numbered list

* Update docs/datadog_monitor.md

Removed highlighting the word namespace for conformity.

Co-authored-by: Celene <[email protected]>

* Update datadog_monitor.md

Adding *Note* on increased memory usage with adding namesapces referenced: #967

* Update docs/datadog_monitor.md

Updates of format for conformity.

Co-authored-by: Celene <[email protected]>

* Update datadog_monitor.md

Re-formatted to reduce repetition of `Note` identifiers.

* Update docs/datadog_monitor.md

Co-authored-by: Celene <[email protected]>

* Update datadog_monitor.md

Removal of [8] reference link.

---------

Co-authored-by: Brett Blue <[email protected]>
Co-authored-by: Celene <[email protected]>

docs/datadog_monitor.md

@@ -52,6 +52,18 @@ To deploy a `DatadogMonitor` with the Datadog Operator, use the [`datadog-operat
 
     For additional examples, see [examples/datadog-monitor](../examples/datadogmonitor). Note that only metric alerts, query alerts, and service checks are supported.
 
+   By default, the Operator only watches its own namespace, so it will manage any `DatadogMonitor` objects within its own namespace. Therefore, you should deploy your Datadog objects in the same namespace as the Operator. If you'd like to deploy your DatadogMonitors in different namespaces, then you will need to configure the Operator [`watchNamespaces`][6] section with those additional namespaces:
+
+   ```yaml
+      #(...)
+      watchNamespaces:
+        - datadog
+        - <NAMESPACE_1>
+        - <NAMESPACE_2>
+        - <NAMESPACE_3>
+   ```
+   *Note:* Adding namespaces increases number of resources the Operator watches. You may need to adjust the memory limits for these addition of namespaces.
+
 1. Deploy the `DatadogMonitor` with the above configuration file:
 
     ```shell