add missing punctuation in lightning_cli.rst (#7554)

Author: loic-beheshti

docs/source/common/lightning_cli.rst

@@ -64,7 +64,7 @@ LightningCLI
 ^^^^^^^^^^^^
 
 The implementation of training command line tools is done via the :class:`~pytorch_lightning.utilities.cli.LightningCLI`
-class. The minimal installation of pytorch-lightning does not include this support. To enable it either install
+class. The minimal installation of pytorch-lightning does not include this support. To enable it, either install
 lightning with the :code:`all` extras require or install the package :code:`jsonargparse[signatures]`.
 
 The case in which the user's :class:`~pytorch_lightning.core.lightning.LightningModule` class implements all required