Update covid_eu_schema.md

schemas/covid_eu_schema.md

@@ -20,9 +20,14 @@ All EU Countries
 | 7 | Covid EU Vaccination Dosage            | Dosage info for vaccination provided, e.g. 1 of 2                   |
 | 8 | Covid EU Certificate Issuer            | Issuer of the vaccination certificate                            |
 
+#### Duplicate check field
+
+Following field value should be used for handling duplicate records:
+
+Covid EU Unique Certificate Identifier
 
 ## Source
 
 * https://ec.europa.eu/health/sites/default/files/ehealth/docs/vaccination-proof_interoperability-guidelines_en.pdf
 * https://ec.europa.eu/info/live-work-travel-eu/coronavirus-response/safe-covid-19-vaccines-europeans/eu-digital-covid-certificate_en 
-* https://www.consilium.europa.eu/en/policies/coronavirus/eu-digital-covid-certificate/ 
+* https://www.consilium.europa.eu/en/policies/coronavirus/eu-digital-covid-certificate/