added update about discriminator support (#4)

Co-authored-by: n.totskii <n.totskiy@fxpro.com>

Author: nt0tsky

docs/faq.md

@@ -31,8 +31,20 @@ A path like `/files/some/long/path` will pass validation. The Express `req.param
 
 ### **Q:** Can I use discriminators with `oneOf` and `anyOf`?
 
-Currently, there is support for top level discriminators. See [top-level discriminator example](https://github.com/cdimascio/express-openapi-validator/tree/master/examples/8-top-level-discriminator)
-
+- By default, only **top-level discriminators** are supported. See the [top-level discriminator example](https://github.com/cdimascio/express-openapi-validator/tree/master/examples/8-top-level-discriminator).
+- To also enable **deep discriminator** support (nested within `oneOf` / `anyOf`), set the `discriminator` option under `validateRequests`:
+
+```js
+app.use(
+    OpenApiValidator.middleware({
+        apiSpec,
+        validateRequests: {
+            discriminator: true,
+            //... other options
+        }
+    })
+);
+```
 ---
 
 ### **Q:** What happened to the `securityHandlers` property?

docs/usage-validate-requests.md

@@ -11,6 +11,7 @@ Determines whether the validator should validate requests.
         coerceTypes: false | true | 'array',
         removeAdditional: false | true | 'all' | 'failing',
         allErrors: false | true,
+        discriminator: false | true,
     }
     ```
 
@@ -100,3 +101,34 @@ Determines whether the validator should validate requests.
 
         - `true` - all rules should be checked and all failures reported
         - `false` - (**default**) stop checking rules after the first failure
+
+    - ### `discriminator`
+    
+      > This option was introduced in version 5.6.0 to extend support for OpenAPI discriminators.
+    
+      Enables validation of schemas that use OpenAPI `discriminator` fields with `oneOf` / `anyOf`.
+    
+      By default, only **top-level discriminators** are supported.  
+      When this option is enabled, the validator also supports **deep (nested) discriminators** inside `oneOf` / `anyOf` structures.
+    
+      **Option Schema**
+        ```javascript
+        discriminator: false | true
+        ```
+    
+        - `true` – enable validation of both top-level and deep discriminators
+        - `false` – (**default**) only top-level discriminators are validated
+    
+      **Example**
+        ```javascript
+        app.use(
+          OpenApiValidator.middleware({
+            apiSpec,
+            validateRequests: {
+              discriminator: true,
+            }
+          })
+        );
+        ```
+        
+