Improve doc strings substitution_probability.py (#3477)

* Update substitution_probability.py

Signed-off-by: J. George <[email protected]>

* Update substitution_probability.py

---------

Signed-off-by: J. George <[email protected]>

Author: JaGeo

pymatgen/analysis/structure_prediction/substitution_probability.py

@@ -85,8 +85,8 @@ def __init__(self, lambda_table=None, alpha=-5):
     def get_lambda(self, s1, s2):
         """
         Args:
-            s1 (Structure): 1st Structure
-            s2 (Structure): 2nd Structure.
+            s1 (Element/Species/str/int): Describes Ion in 1st Structure
+            s2 (Element/Species/str/int): Describes Ion in 2nd Structure.
 
         Returns:
             Lambda values