Clarify devtools trigger file documentation

Closes gh-17775

Author: philwebb

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/autoconfigure/DevToolsProperties.java

@@ -90,8 +90,9 @@ public static class Restart {
 		private Duration quietPeriod = Duration.ofMillis(400);
 
 		/**
-		 * Name of a specific file that, when changed, triggers the restart check. If not
-		 * specified, any classpath file change triggers the restart.
+		 * Name of a specific file that, when changed, triggers the restart check. Must be
+		 * a simple name (without any path) of a file that appears on your classpath. If
+		 * not specified, any classpath file change triggers the restart.
 		 */
 		private String triggerFile;
 

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

@@ -798,13 +798,38 @@ If you need to _completely_ disable restart support (for example, because it doe
 ==== Using a Trigger File
 If you work with an IDE that continuously compiles changed files, you might prefer to trigger restarts only at specific times.
 To do so, you can use a "`trigger file`", which is a special file that must be modified when you want to actually trigger a restart check.
-Changing the file only triggers the check and the restart only occurs if Devtools has detected it has to do something.
-The trigger file can be updated manually or with an IDE plugin.
 
-To use a trigger file, set the `spring.devtools.restart.trigger-file` property to the path of your trigger file.
+NOTE: Any update to the file file will trigger a check, but restart only actually occurs if Devtools has detected it has something to do.
+
+To use a trigger file, set the `spring.devtools.restart.trigger-file` property to the name (excluding any path) of your trigger file.
+The trigger file must appear somewhere on your classpath.
+
+For example, if you have a project with the following structure:
+
+[indent=0]
+----
+	src
+	+- main
+	   +- resources
+	      +- .reloadtrigger
+----
+
+Then your `trigger-file` property would be:
+
+[source,properties,indent=0]
+----
+	spring.devtools.restart.trigger-file=.reloadtrigger
+----
+
+Restarts will now only happen when the `src/main/resources/.reloadtrigger` is updated.
 
 TIP: You might want to set `spring.devtools.restart.trigger-file` as a <<using-boot-devtools-globalsettings,global setting>>, so that all your projects behave in the same way.
 
+Some IDEs have features that save you from needing to update your trigger file manually.
+https://spring.io/tools[Spring Tools for Eclipse] and https://www.jetbrains.com/idea/[IntelliJ IDEA (Ultimate Edition)] both have such support.
+With Spring Tools, you can use the "`reload`" button from the console view (as long as your `trigger-file` is named `.reloadtrigger`).
+For IntelliJ, you can follow the https://www.jetbrains.com/help/idea/spring-boot.html#configure-application-update-policies-with-devtools[instructions in their documentation].
+
 
 
 [[using-boot-devtools-customizing-classload]]