Clarify S3 restore script location
Clarify S3 restore script location

* The `mongodb-restore-s3` only exists on machines which have enabled S3 backups (as configured in govuk-puppet).
* Add a way for readers to ascertain which machines have enabled S3 backups and thus also contain the script.

alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs