Add explicit callout for registering function in function factory

fern/docs/pages/references/functions.mdx

@@ -2,6 +2,7 @@ Using functions, you can provide custom code and link it to your event sources,
 
 In order to create a snap-in version, functions must be defined as shown in the [code samples](/snapin-development/code-samples). Functions are packaged and provided as an artifact at the time of snap-in version creation and then used to deploy functions to snap-in versions. An artifact may contain multiple function definitions. The artifact is a zip file containing the following files:
 
+
 ```bash
 /
 ├── src/
@@ -26,4 +27,9 @@ functions:
 - `name`: It is the function name that should match the corresponding function name in the folder.
 - `description`: It describes the function.
 
+
+<Callout intent="note">
+Each function should be registered in `src/function-factory.ts` to be available for execution.
+</Callout>
+
 Refer to the [function invocation](/snapin-development/references/function-invocation) for details about the exact payload of the function.