[Doc] [runtime env] Add note to install ray[default] (#17869)

doc/source/advanced.rst

@@ -432,6 +432,10 @@ Runtime Environments
 
     This API is in beta and may change before becoming stable.
 
+.. note::
+
+    This feature requires a full installation of Ray using `pip install "ray[default]"`.
+
 On Mac OS and Linux, Ray 1.4+ supports dynamically setting the runtime environment of tasks, actors, and jobs so that they can depend on different Python libraries (e.g., conda environments, pip dependencies) while all running on the same Ray cluster.
 
 The ``runtime_env`` is a (JSON-serializable) dictionary that can be passed as an option to tasks and actors, and can also be passed to ``ray.init()``.