Added single GPU training script for decoder (#108)

Added config files for training

Changed example image generation to be more efficient

Added configuration description to README

Removed unused import

dalle2_pytorch/optimizer.py

@@ -11,7 +11,8 @@ def get_optimizer(
     wd = 1e-2,
     betas = (0.9, 0.999),
     eps = 1e-8,
-    filter_by_requires_grad = False
+    filter_by_requires_grad = False,
+    **kwargs
 ):
     if filter_by_requires_grad:
         params = list(filter(lambda t: t.requires_grad, params))