Update documentation and fix typo
RELNOTES:
@@ -227,5 +227,5 @@ If you really want to override a value, use a separate statement:
When set, arithmetic operations (`+`, `-`, `*`) will fail in case of overflow.
All integers are stored using signed 32 bits.
-* Flag: `--incompatible_incompatible_checked_arithmetic`
-* Default: `false`
+* Flag: `--incompatible_checked_arithmetic`
+* Default: `true`
