Merge pull request #2668 from lianmakesthings/clarify-functions-usage

docs: clarify where functions can be used

Author: FabianKramm

docs/pages/configuration/functions/README.mdx

@@ -43,6 +43,7 @@ pipelines:
     hello_world
     run_default_pipeline dev
 ```
+Please note that custom functions can only be called from `pipelines` and other `functions` as these run in a `pipeline` context.
 
 
 ## Built-In Functions