Add missing entries for overflow-checks to config.toml.example.

Author: hkratz

config.toml.example

@@ -423,6 +423,18 @@ changelog-seen = 2
 # set this value to `true`.
 #debug-logging = rust.debug-assertions (boolean)
 
+# Whether or not overflow checks are enabled for the compiler and standard
+# library.
+#
+# Defaults to rust.debug value
+#overflow-checks = rust.debug (boolean)
+
+# Whether or not overflow checks are enabled for the standard library.
+# Overrides the `overflow-checks` option, if defined.
+#
+# Defaults to rust.overflow-checks value
+#overflow-checks-std = rust.overflow-checks (boolean)
+
 # Debuginfo level for most of Rust code, corresponds to the `-C debuginfo=N` option of `rustc`.
 # `0` - no debug info
 # `1` - line tables only - sufficient to generate backtraces that include line