Improve Metrics Dictionary docs

doc/development/usage_ping/metrics_dictionary.md

@@ -35,14 +35,14 @@ Each metric is defined in a separate YAML file consisting of a number of fields:
 | `value_type`        | yes      | `string`; one of `string`, `number`, `boolean`.                                                               |
 | `status`            | yes      | `string`; status of the metric, may be set to `data_available`, `planned`, `in_progress`, `implemented`, `not_used`, `deprecated` |
 | `time_frame`        | yes      | `string`; may be set to a value like `7d`, `28d`, `all`, `none`. |
-| `data_source`       | yes      | `string`: may be set to a value like `database`, `redis`, `redis_hll`, `prometheus`, `ruby`. |
-| `distribution`      | yes      | The [distribution](https://about.gitlab.com/handbook/marketing/strategic-marketing/tiers/#definitions) where the metric applies. |
-| `tier`              | yes      | The [tier]( https://about.gitlab.com/handbook/marketing/strategic-marketing/tiers/) where the metric applies. |
+| `data_source`       | yes      | `string`; may be set to a value like `database`, `redis`, `redis_hll`, `prometheus`, `ruby`. |
+| `distribution`      | yes      | `array`; may be set to one of `ce, ee` or `ee`. The [distribution](https://about.gitlab.com/handbook/marketing/strategic-marketing/tiers/#definitions) where the tracked feature is available.  |
+| `tier`              | yes      | `array`; may be set to one of `free, premium, ultimate`, `premium, ultimate` or `ultimate`. The [tier]( https://about.gitlab.com/handbook/marketing/strategic-marketing/tiers/) where the tracked feature is available. |
 | `milestone`         | no       | The milestone when the metric is introduced. |
 | `milestone_removed` | no       | The milestone when the metric is removed. |
 | `introduced_by_url` | no       | The URL to the Merge Request that introduced the metric. |
 
-### Example metric definition
+### Example YAML metric definition
 
 The linked [`uuid`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/metrics/license/uuid.yml)
 YAML file includes an example metric definition, where the `uuid` metric is the GitLab
@@ -93,3 +93,9 @@ To create a metric definition used in EE, add the `--ee` flag.
 bundle exec rails generate gitlab:usage_metric_definition counts.issues --ee --dir=7d
 create  ee/config/metrics/counts_7d/issues.yml
 ```
+
+## Metrics added dynamic to Usage Ping payload
+
+The [Redis HLL metrics](../usage_ping.md#known-events-are-added-automatically-in-usage-data-payload) are added automatically to Usage Ping payload.
+
+A YAML metric definition is required for each metric.