Add more config docs

Author: jrauh01

doc/03-Configuration.md

@@ -1,4 +1,4 @@
-# Configuration
+# Configuration via YAML File
 
 The configuration is stored in `/etc/icinga-kubernetes/config.yml`.
 See [config.example.yml](../config.example.yml) for an example configuration.
@@ -9,19 +9,40 @@ Connection configuration for the database to which Icinga for Kubernetes synchro
 This is also the database used in
 [Icinga for Kubernetes Web](https://icinga.com/docs/icinga-kubernetes-web) to view and work with the data.
 
-| Option   | Description                                                        |
-|----------|--------------------------------------------------------------------|
-| type     | **Optional.** Only `mysql` is supported yet which is the default.  |
-| host     | **Required.** Database host or absolute Unix socket path.          |
-| port     | **Optional.** Database port. By default, the MySQL port.           |
-| database | **Required.** Database name.                                       |
-| user     | **Required.** Database username.                                   |
-| password | **Optional.** Database password.                                   |
-| tls      | **Optional.** Whether to use TLS.                                  |
-| cert     | **Optional.** Path to TLS client certificate.                      |
-| key      | **Optional.** Path to TLS private key.                             |
-| ca       | **Optional.** Path to TLS CA certificate.                          |
-| insecure | **Optional.** Whether not to verify the peer.                      |
+| Option   | Description                                                       |
+|----------|-------------------------------------------------------------------|
+| type     | **Optional.** Only `mysql` is supported yet which is the default. |
+| host     | **Required.** Database host or absolute Unix socket path.         |
+| port     | **Optional.** Database port. By default, the MySQL port.          |
+| database | **Required.** Database name.                                      |
+| user     | **Required.** Database username.                                  |
+| password | **Optional.** Database password.                                  |
+| tls      | **Optional.** Whether to use TLS.                                 |
+| cert     | **Optional.** Path to TLS client certificate.                     |
+| key      | **Optional.** Path to TLS private key.                            |
+| ca       | **Optional.** Path to TLS CA certificate.                         |
+| insecure | **Optional.** Whether not to verify the peer.                     |
+
+## Logging Configuration
+
+| Env      | Description                                                                                                                                                              |
+|----------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| level    | **Optional.** Default logging level. Can be set to `fatal`, `error`, `warn`, `info` or `debug`. If not set, defaults to `info`.                                          |
+| output   | **Optional.** Logging output. Can be set to `console` (stderr) or `systemd-journald`. If not set, logs to systemd-journald when running under systemd, otherwise stderr. |
+| interval | **Optional.** Interval for periodic logging defined as duration string. Valid units are `ms`, `s`, `m`, `h`. Defaults to `20s`.                                          |
+
+## Notifications Configuration
+
+Connection configuration for [Icinga Notifications](https://github.com/icinga/icinga-notifications) daemon.
+If one of `url`, `username`, or `password` is set, **all** must be set.
+Defined in the `notifications` section of the configuration file.
+
+| Option             | Description                                                                                           |
+|--------------------|-------------------------------------------------------------------------------------------------------|
+| url                | **Optional.** Icinga Notifications daemon URL. If not set, notifications are disabled                 | 
+| username           | **Optional.** Username for authenticating the Icinga for Kubernetes source in Icinga Notifications.   |
+| password           | **Optional.** Password for authenticating the Icinga for Kubernetes source in Icinga Notifications.   |
+| kubernetes_web_url | **Optional.** The base URL of Icinga for Kubernetes Web used in generated Icinga Notification events. |
 
 ## Prometheus Configuration