Document that spring(Profile|Property) cannot be used with scan=true

Closes gh-5611

Author: wilkinsona

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -1570,6 +1570,16 @@ NOTE: You cannot use extensions in the standard `logback.xml` configuration file
 it's loaded too early. You need to either use `logback-spring.xml` or define a
 `logging.config` property.
 
+WARNING: The extensions cannot be used with Logback's
+http://logback.qos.ch/manual/configuration.html#autoScan[configuration scanning]. If you
+attempt to do so, making changes to the configuration file will result in an error similar
+to once of the following being logged:
+
+----
+ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProperty], current ElementPath is [[configuration][springProperty]]
+ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProfile], current ElementPath is [[configuration][springProfile]]
+----
+
 
 
 ==== Profile-specific configuration