Add a tip about "use server" to action docs

Author: amirhhashemi

src/routes/solid-router/concepts/actions.mdx

@@ -43,6 +43,12 @@ In this example, the `echo` action simulates a fetch call with a 1 second delay
 The `echo` action will act as a backend, however, it can be substituted for any API provided it can be run on the client.
 Typically, route actions are used with some sort of solution like fetch or GraphQL.
 
+<Callout type="tip">
+
+In [SolidStart](/solid-start) apps, it's recommended to use the [`"use server"`](/solid-start/reference/server/use-server) directive to leverage server-side caching.
+
+</Callout>
+
 ### Using actions
 
 To use the action, you can call it from within a component using [`useAction`](/solid-router/reference/data-apis/use-action).

src/routes/solid-router/reference/data-apis/action.mdx

@@ -59,6 +59,12 @@ const deleteTodo = action(async (id: number) => {
 
 ```
 
+<Callout type="tip">
+
+In [SolidStart](/solid-start) apps, it's recommended to use the [`"use server"`](/solid-start/reference/server/use-server) directive to leverage server-side caching.
+
+</Callout>
+
 ## Notes of `<form>` implementation and SSR
 
 This requires stable references because a string can only be serialized as an attribute, and it is crucial for consistency across SSR. where these references must align.