Fix Typo in TBPTT Documentation and Improve Trainer Docstring (#20897)

Author: kilavvy

docs/source-pytorch/common/tbptt.rst

@@ -2,7 +2,7 @@
 Truncated Backpropagation Through Time (TBPTT)
 ##############################################
 
-Truncated Backpropagation Through Time (TBPTT) performs backpropogation every k steps of
+Truncated Backpropagation Through Time (TBPTT) performs backpropagation every k steps of
 a much longer sequence. This is made possible by passing training batches
 split along the time-dimensions into splits of size k to the
 ``training_step``. In order to keep the same forward propagation behavior, all

examples/fabric/build_your_own_trainer/trainer.py

@@ -35,7 +35,7 @@ def __init__(
         checkpoint_dir: str = "./checkpoints",
         checkpoint_frequency: int = 1,
     ) -> None:
-        """Exemplary Trainer with Fabric. This is a very simple trainer focused on readablity but with reduced
+        """Exemplary Trainer with Fabric. This is a very simple trainer focused on readability but with reduced
         featureset. As a trainer with more included features, we recommend using the
         :class:`lightning.pytorch.Trainer`.