Clarify usage of @ImportResource in doc

See gh-8143

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

@@ -3235,7 +3235,7 @@ replacing those elements from the `web.xml` as follows:
   container as if it was a `<servlet/>` and `<servlet-mapping/>` in `web.xml`.
 * A `@Bean` of type `Filter` or `FilterRegistrationBean` behaves similarly (like a
   `<filter/>` and `<filter-mapping/>`.
-* An `ApplicationContext` in an XML file can be added to an `@Import` in your
+* An `ApplicationContext` in an XML file can be added through an `@ImportResource` in your
   `Application`. Or simple cases where annotation configuration is heavily used already
   can be recreated in a few lines as `@Bean` definitions.