Thing actions: Clarify use of ActionOutputs annotation

The current docs are wrong,
see https://github.com/openhab/openhab-core/blob/a22349abf4b3106ec8a3eb9d36799e334cdfbf25/bundles/org.openhab.core.automation/src/main/java/org/openhab/core/automation/module/provider/AnnotationActionModuleTypeHelper.java#L146-L159 for core implementation.

Signed-off-by: Florian Hotze <dev@florianhotze.com>

developers/bindings/index.md

@@ -631,7 +631,11 @@ This is to support the old DSL rules engine and make the action available there.
 
 Each parameter of an action member method must be annotated with `@ActionInput`.
 
-If you return values, you do so by returning a `Map<String,Object>` and annotate the method itself with as many `@ActionOutput`s as you will return map entries.
+If you return values, you do so by returning a `Map<String,Object>` and annotate the method itself with `@ActionOutputs` containing as many `@ActionOutput`s as you will return map entries, e.g.
+
+```java
+@ActionOutputs({ @ActionOutput(name = "foo", label = "Foo", type = "java.lang.String"), @ActionOutput(name = "bar", label = "Bar", type = "java.lang.String") })
+```
 
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