Tweak docs on Maven resource filtering

Fixes gh-1816

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

@@ -177,9 +177,9 @@ placeholders in `application.properties`, e.g.
 
 TIP: If you are inheriting from the `spring-boot-starter-parent` POM, the default filter
 token of the `maven-resources-plugins` has been changed from `+${*}+` to `@` (i.e.
-`@maven.token@` instead of `${maven.token}`) as the former conflicts with those
-placeholders. If you have enabled the maven filtering for the `application.properties`
-directly, you may want to change the default filter token to use
+`@maven.token@` instead of `${maven.token}`) to prevent conflicts with Spring-style
+placeholders. If you have enabled maven filtering for the `application.properties`
+directly, you may want to also change the default filter token to use
 http://maven.apache.org/plugins/maven-resources-plugin/resources-mojo.html#delimiters[other delimiters].
 
 NOTE: In this specific case the port binding will work in a PaaS environment like Heroku

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

@@ -42,7 +42,12 @@ defaults. The parent project provides the following features:
   http://maven.apache.org/surefire/maven-surefire-plugin/[surefire],
   https://github.com/ktoso/maven-git-commit-id-plugin[Git commit ID],
   http://maven.apache.org/plugins/maven-shade-plugin/[shade]).
+* Sensible resource filtering for `application.properties` and `application.yml`
 
+On the last point: since the default config files files accept
+Spring style placeholders (`${...}`) the Maven filtering is changed to
+use `@..@` placeholders (you can override that with a Maven property
+`resource.delimiter`).
 
 
 [[using-boot-maven-parent-pom]]