Added encoder forward explanation

              sa_dropout_p: float = 0.0) -> torch.Tensor:

    """Output computation for the MATEncoder layer.

    In the MATEncoderLayer intialization, self.sublayer is defined as an nn.ModuleList of 2 layers. We will be passing our computation through these layers sequentially.

    nn.ModuleList is subscriptable and thus we can access it as self.sublayer[0], for example.

    Parameters

    ----------

    x: torch.Tensor