doc: first pass on objectwrap documentation

PR-URL: nodejs/node-addon-api#321
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

doc/class_property_descriptor.md

@@ -1,5 +1,36 @@
-# Class propertry and descriptior
+# Class propertry and descriptor
 
-You are reading a draft of the next documentation and it's in continuous update so
-if you don't find what you need please refer to:
-[C++ wrapper classes for the ABI-stable C APIs for Node.js](https://nodejs.github.io/node-addon-api/)
+Property descriptor for use with `Napi::ObjectWrap::DefineClass()`.
+This is different from the standalone `Napi::PropertyDescriptor` because it is
+specific to each `Napi::ObjectWrap<T>` subclass.
+This prevents using descriptors from a different class when defining a new class
+(preventing the callbacks from having incorrect `this` pointers).
+
+## Methods
+
+### Contructor
+
+Creates new instance of `Napi::ClassPropertyDescriptor` descriptor object.
+
+```cpp
+Napi::ClassPropertyDescriptor(napi_property_descriptor desc) : _desc(desc) {}
+```
+
+- `[in] desc`: The `napi_property_descriptor`
+
+Returns new instance of `Napi::ClassPropertyDescriptor` that is used as property descriptor
+inside the `Napi::ObjectWrap<T>` class.
+
+### Operator
+
+```cpp
+operator napi_property_descriptor&() { return _desc; }
+```
+
+Returns the original N-API `napi_property_descriptor` wrapped inside the `Napi::ClassPropertyDescriptor`
+
+```cpp
+operator const napi_property_descriptor&() const { return _desc; }
+```
+
+Returns the original N-API `napi_property_descriptor` wrapped inside the `Napi::ClassPropertyDescriptor`