Polish

Add missing documentation

See gh-4220

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -94,6 +94,7 @@ content into your application; rather pick only the properties that you need.
 	spring.mvc.locale= # set fixed locale, e.g. en_UK
 	spring.mvc.date-format= # set fixed date format, e.g. dd/MM/yyyy
 	spring.mvc.favicon.enabled=true
+	spring.mvc.media-types.*= # Maps file extensions to media types for content negotiation.
 	spring.mvc.message-codes-resolver-format= # PREFIX_ERROR_CODE / POSTFIX_ERROR_CODE
 	spring.mvc.ignore-default-model-on-redirect=true # If the the content of the "default" model should be ignored redirects
 	spring.view.prefix= # MVC view prefix