Clarify formatting recommendations for configuration property javadoc

This commit adds a note to spring-boot-features.adoc to clarify that
using javadoc tags to format configuration property descriptions is not
supported.

See gh-18578

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

@@ -7118,6 +7118,9 @@ Here are some rules we follow internally to make sure descriptions are consisten
 * Use `java.time.Duration` rather than `long` and describe the default unit if it differs from milliseconds, e.g. "If a duration suffix is not specified, seconds will be used".
 * Do not provide the default value in the description unless it has to be determined at runtime.
 
+NOTE: You should only use simple text with `@ConfigurationProperties` field Javadoc, since
+they are not processed before being added to the JSON.
+
 Make sure to <<appendix-configuration-metadata#configuration-metadata-annotation-processor,trigger meta-data generation>> so that IDE assistance is available for your keys as well.
 You may want to review the generated metadata (`META-INF/spring-configuration-metadata.json`) to make sure your keys are properly documented.
 Using your own starter in a compatible IDE is also a good idea to validate that quality of the metadata.