docs: Document the new str.strip() feature
@@ -1430,6 +1430,8 @@ are immutable, all operations return their results as a new string.
specified as the argument
- `strip()` removes whitespace at the beginning and end of the string
+ *(added 0.43.0)* optionally can take one positional string argument,
+ and all characters in that string will be stripped
- `to_int` returns the string converted to an integer (error if string
is not a number)
