Update documentation to describe current limitations

Author: krodak

Sources/JavaScriptKit/Documentation.docc/Articles/BridgeJS/Exporting-Swift/Exporting-Swift-Protocols.md

@@ -190,3 +190,20 @@ When you pass a JavaScript object implementing a protocol to Swift:
 | Protocol inheritance | ❌ |
 | Protocol composition: `Protocol1 & Protocol2` | ❌ |
 | Generics | ❌ |
+
+### Type Support for Protocol Method Parameters and Return Types
+
+Protocol method parameters and return values have more limited type support compared to regular exported Swift functions and classes.
+
+**Supported Types:**
+- Primitives: `Bool`, `Int`, `Float`, `Double`
+- `String`
+- `JSObject`
+
+**Not Supported:**
+- `@JS class` types
+- `@JS enum` types (case, raw value, or associated value)
+- `@JS protocol` types
+- Optional types: `Int?`, `String?`, etc.
+
+> Note: For regular `@JS func` and `@JS class` exports (not within protocols), all these types including optionals, enums, and classes are fully supported. See <doc:Exporting-Swift-Function> and <doc:Exporting-Swift-Optional> for more information.