Add obj decorator

Author: Kevan Stannard

misc_docs/syntax/decorator_obj.mdx

@@ -0,0 +1,35 @@
+---
+id: "obj-decorator"
+keywords: ["obj", "decorator"]
+name: "@obj"
+summary: "This is the `@obj` decorator."
+category: "decorators"
+---
+
+The `@obj` decorator is used to create functions that return JavaScript objects
+with properties that match the function's parameter labels.
+
+### Example
+
+<CodeTab labels={["ReScript", "JS Output"]}>
+
+```res
+@bs.obj
+external action: (~name: string, unit) => _ = ""
+
+let helloAction = action(~name="Hello")
+```
+
+```js
+function helloAction(param) {
+  return {
+    name: "Hello",
+  }
+}
+```
+
+</CodeTab>
+
+### References
+
+* [Convert External into JS Object Creation Function](/docs/manual/latest/generate-converters-accessors#convert-external-into-js-object-creation-function)