Add instructions to create a token for DASHBOARD_GITLAB_API_TOKEN

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

README.md

@@ -5,6 +5,17 @@ from upstreams (Debian, or Apertis itself for downstreams) and aggregates the
 information in a dashboard flagging any incosistency and reporting available
 updated that can be pulled from upstreams.
 
+## Credentials
+
+The dashboard pipeline requires special permissions to access repositories and
+to trigger pipelines, the variable `DASHBOARD_GITLAB_API_TOKEN` must be defined
+with an [access token for the `pkg/` group](https://gitlab.apertis.org/groups/pkg/-/settings/access_tokens)
+with the following parameters:
+
+- `Token name`: `dashboard`
+- `Role`: `Maintainer`
+- `Scope`: `api`
+
 ## Usage
 
 The pipeline runs automatically on a regular schedule.