Fixed a small typo in the cnn.py (#153)

Change weight initialization statement from Xavier to Kaiming

Author: CCanxue

rsl_rl/networks/cnn.py

@@ -147,7 +147,7 @@ def output_dim(self) -> tuple[int, int] | int:
         return self._output_dim
 
     def init_weights(self) -> None:
-        """Initialize the weights of the CNN with Xavier initialization."""
+        """Initialize the weights of the CNN with Kaiming initialization."""
         for idx, module in enumerate(self):
             if isinstance(module, nn.Conv2d):
                 torch.nn.init.kaiming_normal_(module.weight)