Update doc

Author: jwierzbo

docs/design/README.md

@@ -14,3 +14,5 @@
 - [Topology awareness](./topology_awareness.md)
 - [Configuring timezone](./configuring_tz.md)
 - [Operator API](./api.md)
+- [Logging](./logging.md)
+

docs/design/logging.md

@@ -0,0 +1,43 @@
+# Logging configuration
+
+## Operator logging
+
+### Log level
+
+To adjust logging level of the operator, you can use `operator.args` in chart template value 
+as described in [Additional configuration](./additional_configuration.md).
+
+For example, to set log level to `INFO` and `DEBUG` for `requests` package, you can use the following value:
+```yaml
+operator:
+  args: ["--log.level=INFO", "--log.level=requests=DEBUG"]
+```
+
+### Log format
+
+By default, operator logs in `pretty` format.
+
+To switch logging format to the JSON, you can use `operator.args` in chart template value:
+```yaml
+operator:
+  args: ["--log.prettifyLog=false"]
+```
+
+## ArangoDeployment logging
+
+By default, ArangoDeployment logs in `pretty` format.
+
+To switch logging format to the JSON we need to pass `--log.use-json-format` argument to the ArangoDB server in the deployment:
+```yaml
+apiVersion: database.arangodb.com/v1
+kind: ArangoDeployment
+metadata:
+  name: single
+spec:
+  mode: Single
+  single:
+    args:
+      - --log.use-json-format
+      - --log.level=INFO
+      - --log.level=backup=TRACE
+```