Small typo in readme (contraining => constraining) (#1096)

README.md

@@ -1815,7 +1815,7 @@ class ZodType<
 > { ... }
 ```
 
-By contraining these in your generic input, you can limit what schemas are allowable as inputs to your function:
+By constraining these in your generic input, you can limit what schemas are allowable as inputs to your function:
 
 ```ts
 function makeSchemaOptional<T extends z.ZodType<string>>(schema: T) {