Mention that parse_san is not strict (#931)

Author: niklasf

chess/__init__.py

@@ -2980,7 +2980,8 @@ def parse_san(self, san: str) -> Move:
         algebraic notation and returns the corresponding move object.
 
         Ambiguous moves are rejected. Overspecified moves (including long
-        algebraic notation) are accepted.
+        algebraic notation) are accepted. Some common syntactical deviations
+        are also accepted.
 
         The returned move is guaranteed to be either legal or a null move.