Add note about release link uniqueness constraints

Updates the release asset link documentation to indicate that link
names and URLs must be unique within the context of a release.

doc/api/releases/index.md

@@ -365,8 +365,8 @@ POST /projects/:id/releases
 | `ref`              | string          | yes, if `tag_name` doesn't exist | If a tag specified in `tag_name` doesn't exist, the release will be created from `ref` and tagged with `tag_name`. It can be a commit SHA, another tag name, or a branch name. |
 | `milestones`       | array of string | no                          | The title of each milestone the release is associated with. [GitLab Premium](https://about.gitlab.com/pricing/) customers can specify group milestones.                                                                      |
 | `assets:links`     | array of hash   | no                          | An array of assets links.                                                                                                        |
-| `assets:links:name`| string          | required by: `assets:links` | The name of the link.                                                                                                            |
-| `assets:links:url` | string          | required by: `assets:links` | The URL of the link.                                                                                                             |
+| `assets:links:name`| string          | required by: `assets:links` | The name of the link. Link names must be unique within the release.                                                              |
+| `assets:links:url` | string          | required by: `assets:links` | The URL of the link. Link URLs must be unique within the release.                                                                |
 | `assets:links:filepath` | string     | no | Optional path for a [Direct Asset link](../../user/project/releases/index.md#permanent-links-to-release-assets).
 | `assets:links:link_type` | string     | no | The type of the link: `other`, `runbook`, `image`, `package`. Defaults to `other`.
 | `released_at`      | datetime        | no                          | The date when the release will be/was ready. Defaults to the current time. Expected in ISO 8601 format (`2019-03-15T08:00:00Z`). |

doc/api/releases/links.md

@@ -91,14 +91,14 @@ Create an asset as a link from a Release.
 POST /projects/:id/releases/:tag_name/assets/links
 ```
 
-| Attribute     | Type           | Required | Description                             |
-| ------------- | -------------- | -------- | --------------------------------------- |
-| `id`          | integer/string | yes      | The ID or [URL-encoded path of the project](../README.md#namespaced-path-encoding). |
-| `tag_name`    | string         | yes      | The tag associated with the Release. |
-| `name`        | string         | yes      | The name of the link. |
-| `url`         | string         | yes      | The URL of the link. |
-| `filepath` | string     | no | Optional path for a [Direct Asset link](../../user/project/releases/index.md#permanent-links-to-release-assets).
-| `link_type`        | string         | no       | The type of the link: `other`, `runbook`, `image`, `package`. Defaults to `other`. |
+| Attribute     | Type           | Required | Description                                                                                                      |
+| ------------- | -------------- | -------- | ---------------------------------------------------------------------------------------------------------------- |
+| `id`          | integer/string | yes      | The ID or [URL-encoded path of the project](../README.md#namespaced-path-encoding).                              |
+| `tag_name`    | string         | yes      | The tag associated with the Release.                                                                             |
+| `name`        | string         | yes      | The name of the link. Link names must be unique within the release.                                              |
+| `url`         | string         | yes      | The URL of the link. Link URLs must be unique within the release.                                                |
+| `filepath`    | string         | no       | Optional path for a [Direct Asset link](../../user/project/releases/index.md#permanent-links-to-release-assets). |
+| `link_type`   | string         | no       | The type of the link: `other`, `runbook`, `image`, `package`. Defaults to `other`.                               |
 
 Example request: