sagemathgh-36818: Corrected the typo in documentation - Permutation G…

…roups

    
Fixes sagemath#36817

Updated documentation to correct grammatical error in the description of
PermutationGroup, changing 'method' to 'methods'.
    
URL: sagemath#36818
Reported by: Viraj Paradkar
Reviewer(s): Dima Pasechnik

src/sage/groups/perm_gps/permgroup.py

@@ -29,7 +29,7 @@
 Index of methods
 ----------------
 
-Here are the method of a :func:`PermutationGroup`
+Here are the methods of a :func:`PermutationGroup`
 
 {METHODS_OF_PermutationGroup_generic}