Add docstrings to Test Tube logger (#9110)

Author: bamblebam

pytorch_lightning/loggers/test_tube.py

@@ -197,17 +197,35 @@ def close(self) -> None:
 
     @property
     def save_dir(self) -> Optional[str]:
+        """
+        Gets the save directory.
+
+        Returns:
+            The path to the save directory.
+        """
         return self._save_dir
 
     @property
     def name(self) -> str:
+        """
+        Gets the experiment name.
+
+        Returns:
+             The experiment name if the experiment exists, else the name specified in the constructor.
+        """
         if self._experiment is None:
             return self._name
 
         return self.experiment.name
 
     @property
     def version(self) -> int:
+        """
+        Gets the experiment version.
+
+        Returns:
+             The experiment version if the experiment exists, else the next version.
+        """
         if self._experiment is None:
             return self._version