README: Add note for Item & Quantity conversion to Java counterpart

Reference openhab/openhab-addons#14335.

Signed-off-by: Florian Hotze <florianh_dev@icloud.com>

README.md

@@ -334,7 +334,8 @@ If an API does not provide type definitions and therefore autocompletion won't w
 
 ### Items
 
-The Items namespace allows interactions with openHAB items.
+The `items` namespace allows interactions with openHAB Items.
+Anywhere that a native openHAB `Item` is required, the runtime will automatically convert the JS-`Item` to its Java counterpart.
 
 See [openhab-js : items](https://openhab.github.io/openhab-js/items.html) for full API documentation.
 
@@ -913,6 +914,7 @@ A Quantity consists of a measurement and its [Unit of Measurement (UoM)](https:/
 
 Internally using the openHAB `QuantityType`, which relies on [`javax.measure`](https://unitsofmeasurement.github.io/unit-api/), it supports all units and dimensions that openHAB supports.
 If your unit is not listed in the UoM docs, it is very likely that it is still supported, e.g. the Angstrom Å for very small lengths (1 Å = 10 nm).
+Anywhere that a native openHAB `QuantityType` is required, the runtime will automatically convert the JS-`Quantity` to its Java counterpart.
 
 #### Creation