docs: add coercion note to fix compile errors (#4940)

* docs: add coercion note to fix compile errors

see #4938

* Tweaks

---------

Co-authored-by: Colin McDonnell <[email protected]>

Author: rburgst

packages/docs/content/api.mdx

@@ -37,6 +37,7 @@ z.coerce.bigint();    // BigInt(input)
 
 The coerced variant of these schemas attempts to convert the input value to the appropriate type.
 
+
 ```ts
 const schema = z.coerce.string();
 
@@ -46,6 +47,16 @@ schema.parse(true);      // => "true"
 schema.parse(null);      // => "null"
 ```
 
+The input type of these coerced schemas is `unknown` by default. To specify a more specific input type, pass a generic parameter:
+
+```ts
+const A = z.coerce.number();
+type AInput = z.infer<typeof A>; // => number
+
+const B = z.coerce.number<number>();
+type BInput = z.infer<typeof B>; // => number
+```
+
 <Accordions type="single"><Accordion title="How coercion works in Zod">
 
   Zod coerces all inputs using the built-in constructors.