docs: fix registry server configuration example in README (#328, #329)

Author: AJWavio

README.md

@@ -167,9 +167,9 @@ services:
     image: registry:2.8.2
     restart: always
     environment:
-      REGISTRY_HTTP_HEADERS_Access-Control-Origin: '[http://registry.example.com]'
+      REGISTRY_HTTP_HEADERS_Access-Control-Allow-Origin: '[http://registry.example.com]'
       REGISTRY_HTTP_HEADERS_Access-Control-Allow-Methods: '[HEAD,GET,OPTIONS,DELETE]'
-      REGISTRY_HTTP_HEADERS_Access-Control-Credentials: '[true]'
+      REGISTRY_HTTP_HEADERS_Access-Control-Allow-Credentials: '[true]'
       REGISTRY_HTTP_HEADERS_Access-Control-Allow-Headers: '[Authorization,Accept,Cache-Control]'
       REGISTRY_HTTP_HEADERS_Access-Control-Expose-Headers: '[Docker-Content-Digest]'
       REGISTRY_STORAGE_DELETE_ENABLED: 'true'