Clarify that the `production` environment is case-sensitive

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/22533

doc/user/project/cycle_analytics.md

@@ -65,7 +65,7 @@ Below you can see in more detail what the various stages of Cycle Analytics mean
 | Code      | Measures the median time between pushing a first commit (previous stage) and creating a merge request related to that commit. The key to keep the process tracked is to include the [issue closing pattern] to the description of the merge request (for example, `Closes #xxx`, where `xxx` is the number of the issue related to this merge request). If the issue closing pattern is not present in the merge request description, the MR is not considered to the measurement time of the stage. |
 | Test      | Measures the median time to run the entire pipeline for that project. It's related to the time GitLab CI takes to run every job for the commits pushed to that merge request defined in the previous stage. It is basically the start->finish time for all pipelines. `master` is not excluded. It does not attempt to track time for any particular stages. |
 | Review    | Measures the median time taken to review the merge request, between its creation and until it's merged. |
-| Staging   | Measures the median time between merging the merge request until the very first deployment to production. It's tracked by the [environment] set to `production` in your GitLab CI configuration. If there isn't a `production` environment, this is not tracked. |
+| Staging   | Measures the median time between merging the merge request until the very first deployment to production. It's tracked by the [environment] set to `production` (case-sensitive, `Production` won't work) in your GitLab CI configuration. If there isn't a `production` environment, this is not tracked. |
 | Production| The sum of all time taken to run the entire process, from issue creation to deploying the code to production. |
 
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