[DOCS] Added sysgenkey command and watcher settings

Original commit: elastic/x-pack-elasticsearch@8e0b2027a6

docs/en/commands/index.asciidoc

@@ -9,10 +9,12 @@
 
 * <<certgen>>
 * <<setup-passwords>>
+* <<syskeygen>>
 * <<users-command>>
 
 --
 
 include::certgen.asciidoc[]
 include::setup-passwords.asciidoc[]
+include::syskeygen.asciidoc[]
 include::users-command.asciidoc[]

docs/en/commands/syskeygen.asciidoc

@@ -0,0 +1,60 @@
+[role="xpack"]
+[[syskeygen]]
+== syskeygen
+
+The `syskeygen` command creates a system key file in
+`CONFIG_DIR/x-pack/system_key`. You can then copy the generated system key to
+the rest of the nodes in the cluster.
+
+//TBD: Why?  What's its purpose?
+
+IMPORTANT: The system key is a symmetric key, so the same key must be on every
+node in the cluster. You must also ensure that the file permissions are set
+such that the key can be read by the user that {es} runs as.
+
+[float]
+=== Synopsis
+
+[source,shell]
+--------------------------------------------------
+bin/x-pack/syskeygen
+[-E <KeyValuePair>] [-h, --help]
+([-s, --silent] | [-v, --verbose])
+--------------------------------------------------
+
+[float]
+=== Description
+
+Encryption of sensitive data requires a key. For example, if you enable the
+<<notification-settings,`xpack.watcher.encrypt_sensitive_data` setting>>,
+//TBD: Can we clarify what type of sensitive data is encrypted when this is enabled?
+you must also create a system key file and place it in the secure setting store.
+After you run the `syskeygen` command, run the
+`elasticsearch-keystore add-file xpack.watcher.encryption_key <filepath>`
+command. Finally, remove the `system_key` file from the filesystem. Repeat these
+steps on every node in the cluster.
+
+//TBD: Are there other scenarios where you could use this system file?
+
+[float]
+=== Parameters
+
+`-E <KeyValuePair>`:: Configures a setting.
+
+`-h, --help`:: Returns all of the command parameters.
+
+`-s, --silent`:: Shows minimal output.
+
+`-v, --verbose`:: Shows verbose output.
+
+////
+[float]
+=== Examples
+
+//TBD: What's an example of a -E value that we might use in this command?
+
+[source, sh]
+--------------------------------------------------
+bin/x-pack/syskeygen
+--------------------------------------------------
+////

docs/en/settings/notification-settings.asciidoc

@@ -5,10 +5,16 @@
 <titleabbrev>{watcher} Settings</titleabbrev>
 ++++
 
-You configure `xpack.notification` settings in `elasticsearch.yml` to
-send set up {watcher} and send notifications via <<email-notification-settings, email>>,
-<<hipchat-notification-settings, HipChat>>, <<slack-notification-settings,
-Slack>>, and <<pagerduty-notification-settings, PagerDuty>>.
+You configure {watcher} settings to set up {watcher} and send notifications via
+<<email-notification-settings,email>>,
+<<hipchat-notification-settings,HipChat>>,
+<<slack-notification-settings,Slack>>, and
+<<pagerduty-notification-settings, PagerDuty>>.
+
+All of these settings can be added to the `elasticsearch.yml` configuration file,
+with the exception of the secure settings, which you add to the {es} keystore.
+For more information about creating and updating the {es} keystore, see
+<<secure-settings>>.
 
 [float]
 [[general-notification-settings]]
@@ -16,6 +22,20 @@ Slack>>, and <<pagerduty-notification-settings, PagerDuty>>.
 `xpack.watcher.enabled`::
 Set to `false` to disable {watcher} on the node.
 
+`xpack.watcher.encrypt_sensitive_data` (<<secure-settings,Secure>>)::
+Set to `true` to encrypt sensitive data. If this setting is enabled, you
+must also specify the `xpack.watcher.encryption_key` setting.
+//TBD: Can we be more specific about what type of watcher data it's encrypting?
+
+`xpack.watcher.encryption_key` (<<secure-settings,Secure>>)::
+Specifies the path to a file that contains a key for encrypting sensitive data.
+If `xpack.watcher.encrypt_sensitive_data` is set to `true`, this setting is
+required. For example, to generate the key file, run the <<syskeygen>> tool.
+Then import the key into the secure setting store with the
+`elasticsearch-keystore add-file xpack.watcher.encryption_key <filepath>`
+command. Finally, remove the system_key file from the filesystem. Repeat this on
+every node in the cluster. 
+
 `xpack.watcher.history.cleaner_service.enabled`::
 Set to `false` (default) to disable the cleaner service, which removes previous
 versions of {watcher} indices (for example, .watcher-history*) when it