Merge pull request #2351 from alphagov/update-docs-for-fact-check-met…

…rics

Add note on fact-check email metrics

docs/fact-checking.md

@@ -10,3 +10,5 @@ Publisher comes with a system to allow editions not yet published to be external
 1. Every 5 minutes, the [mail_fetcher](../script/mail_fetcher) script runs which reads any new emails from the inbox, parses the response and adds it to the edition in the database.
 
 **Note:** The ID of the edition is included in the subject line of the fact check email. It's important that this is never removed, otherwise the app will be [unable to match the email with the edition](https://docs.publishing.service.gov.uk/manual/alerts/publisher-unprocessed-fact-check-emails.html).
+
+**Information:** Sometimes fact check emails will fail to be processed. We use Prometheus to report this, and you can see how many are currently in the production fact-check inbox using [this grafana page](https://grafana.eks.production.govuk.digital/explore?schemaVersion=1&panes=%7B%22fj9%22%3A%7B%22datasource%22%3A%22prometheus%22%2C%22queries%22%3A%5B%7B%22refId%22%3A%22A%22%2C%22expr%22%3A%22publisher_fact_check_unprocessed_emails_total%22%2C%22range%22%3Atrue%2C%22instant%22%3Atrue%2C%22datasource%22%3A%7B%22type%22%3A%22prometheus%22%2C%22uid%22%3A%22prometheus%22%7D%2C%22editorMode%22%3A%22code%22%2C%22legendFormat%22%3A%22unprocessed_emails%22%7D%5D%2C%22range%22%3A%7B%22from%22%3A%22now-30d%22%2C%22to%22%3A%22now%22%7D%7D%7D&orgId=1).