docs: Ranger21 docstring

Author: kozistr

pytorch_optimizer/optimizer/ranger21.py

@@ -15,6 +15,19 @@
 
 class Ranger21(Optimizer, BaseOptimizer):
     r"""Integrating the latest deep learning components into a single optimizer.
+        Here's the components
+            * uses the AdamW optimizer as its core (or, optionally, MadGrad)
+            * Adaptive gradient clipping
+            * Gradient centralization
+            * Positive-Negative momentum
+            * Norm loss
+            * Stable weight decay
+            * Linear learning rate warm-up
+            * Explore-exploit learning rate schedule
+            * Lookahead
+            * Softplus transformation
+            * Gradient Normalization
+            * Corrects the denominator (AdamD)
 
     :param params: PARAMETERS. iterable of parameters to optimize or dicts defining parameter groups.
     :param lr: float. learning rate.