Explain the displayed pipeline duration

doc/ci/pipelines/cicd_minutes.md

@@ -149,7 +149,7 @@ namespace.
 
 ## How CI/CD minutes are calculated
 
-CI/CD minutes are calculated based on:
+CI/CD minutes for individual jobs are calculated based on:
 
 - The duration the job runs.
 - The visibility of the projects where the job runs.
@@ -174,6 +174,10 @@ For example:
 - If a pipeline runs for one of the personal projects for `alice`, the CI/CD minutes
   are added to the overall consumption for the `alice` namespace.
 
+The CI/CD minutes used by one pipeline is the total CI/CD minutes used by all the jobs
+that ran in the pipeline. The CI/CD minute usage for a pipeline can be higher than
+the duration of the pipeline if many jobs ran at the same time.
+
 ### Cost factor
 
 The cost factor for a job running on a shared runner is: