Fix formatting for example code in chess docstring (doctest) (#1013)

pettingzoo/classic/chess/chess.py

@@ -71,11 +71,13 @@
 
 You can get back the original (x,y,c) coordinates from the integer action `a` with the following expression: `(a // (8*73), (a // 73) % 8, a % (8*73) % 73)`
 
-> x = 6
-> y = 0
-> c = 12
-> a = x*(8*73) + y*73 + c
-> print(a // (8*73), a % (8*73) // 73, a % (8*73) % 73)  # -> 6 0 12
+Example:
+    >>> x = 6
+    >>> y = 0
+    >>> c = 12
+    >>> a = x*(8*73) + y*73 + c
+    >>> print(a // (8*73), a % (8*73) // 73, a % (8*73) % 73)
+    6 0 12
 
 Note: the coordinates (6, 0, 12) correspond to column 6, row 0, plane 12. In chess notation, this would signify square G1: