doc: n-api: out params for TypedArray info can be NULL

This is useful information to have for applications that don't need to read the other properties. The implementation checks for `nullptr`, see: https://github.com/nodejs/node/blob/master/src/js_native_api_v8.cc#L2879

doc/api/n-api.md

@@ -2820,6 +2820,8 @@ napi_status napi_get_typedarray_info(napi_env env,
 Returns `napi_ok` if the API succeeded.
 
 This API returns various properties of a typed array.
+
+Any of the out parameters may be `NULL` if that property is unneeded.
 
 *Warning*: Use caution while using this API since the underlying data buffer
 is managed by the VM.
@@ -2850,6 +2852,8 @@ napi_status napi_get_dataview_info(napi_env env,
   to start projecting the `DataView`.
 
 Returns `napi_ok` if the API succeeded.
+  
+Any of the out parameters may be `NULL` if that property is unneeded.
 
 This API returns various properties of a `DataView`.