Fixed Import in Docs For Multinode Trainer Name Which does Not Exist (#15663)

Author: rlizzo

docs/source-app/levels/basic/hello_components/pl_multinode.py

@@ -1,6 +1,6 @@
 # app.py
 import lightning as L
-from lightning.app.components import PyTorchLightningMultiNode
+from lightning.app.components import LightningTrainerMultiNode
 from lightning.pytorch.demos.boring_classes import BoringModel
 
 
@@ -12,7 +12,7 @@ def run():
         trainer.fit(model)
 
 # 8 GPU: (2 nodes of 4 x v100)
-component = PyTorchLightningMultiNode(
+component = LightningTrainerMultiNode(
     LightningTrainerDistributed,
     num_nodes=2,
     cloud_compute=L.CloudCompute("gpu-fast-multi"), # 4 x v100