Add docs to custom labels page

docs/GENERATE_CUSTOM_LABELS.md

@@ -18,12 +18,26 @@ When running the `generate_labels` tool on a PR that includes changes in SQL que
 
 Note that in addition to the dedicated tool `generate_labels`, the custom labels will also be used by the `review` and `describe` tools.
 
-#### CLI
+#### 1. CLI
 To enable custom labels, you need to apply the [configuration changes](#configuration-changes) to the [custom_labels file](./../pr_agent/settings/custom_labels.toml):
 
-#### GitHub Action and GitHub App
+#### 2. GitHub Action and GitHub App
 To enable custom labels, you need to apply the [configuration changes](#configuration-changes) to the local `.pr_agent.toml` file in you repository.
 
+#### 3. Git provider's native labels page (Pr-Agent Pro feature :gem:) 
+To enable custom labels, you can add/edit the custom labels in the Git provider's native labels page. For example, in GitHub, you can add/edit the labels in the Labels page:   
+a. Go to the Labels page:
+* Github : https://github.com/{owner}/{repo}/labels, or click on the "Labels" tab in the issues or PRs page.
+* GitLab : https://gitlab.com/{owner}/{repo}/-/labels, or click on "Manage" -> "Labels" on the left menu.
+
+b. Add/edit the custom labels. It should be formatted as follows:
+* Label name: The name of the custom label.
+* Description: Description of with prefix `pr_agent:`, for example: `pr_agent: Description of when AI should suggest this label`.
+<kbd><img src=https://codium.ai/images/pr_agent/add_native_custom_labels.png width="768"></kbd>
+
+c. Now the custom labels will be included in the `generate_labels` tool.
+*This feature is supported in GitHub and GitLab.
+
 #### Configuration changes
  - Change `enable_custom_labels` to True: This will turn off the default labels and enable the custom labels provided in the custom_labels.toml file.
  - Add the custom labels. It should be formatted as follows: