DOC: update the docstring of the group_rank method pandas-dev#20561

Author: peterpanmj

pandas/_libs/groupby_helper.pxi.in

@@ -428,14 +428,20 @@ def group_rank_{{name}}(ndarray[float64_t, ndim=2] out,
     is_datetimelike : bool
         unused in this method but provided for call compatibility with other
         Cython transformations
-    ties_method :  {'keep', 'top', 'bottom'}
-        * keep: leave NA values where they are
-        * top: smallest rank if ascending
-        * bottom: smallest rank if descending
+    ties_method : {'average', 'min', 'max', 'first', 'dense'}
+        * average: average rank of group
+        * min: lowest rank in group
+        * max: highest rank in group
+        * first: ranks assigned in order they appear in the array
+        * dense: like 'min', but rank always increases by 1 between groups
     ascending : boolean
         False for ranks by high (1) to low (N)
     pct : boolean
         Compute percentage rank of data within each group
+    na_option : {'keep', 'top', 'bottom'}
+        * keep: leave NA values where they are
+        * top: smallest rank if ascending
+        * bottom: smallest rank if descending
 
     Notes
     -----