KR resources documentation + Chess tutorial link (#1675)

* Added KR resources documentation

* Adds KorGE Chess tutorial and code

docs/korge/reference/resources/index.md

@@ -10,6 +10,19 @@ KorGE uses the [Virtual File Systems from Korio](/korio/) to load resources from
 and its most basic resources are [Bitmaps from KorIM](/korim/) and [Sounds from KorAU](/korau/).
 But it can also load bitmap fonts, tiled maps, etc.
 
+## `KR`
+
+Since KorGE 4.0.3, there is a new autogenerated class called `KR`. This is similar to Android `R`,
+and provides a type-safe way of accessing resources. It exposes all the files in the resources folder,
+and provides reading shortcuts for images and sounds. In the case of folders ended with `.atlas` it generates
+automatically an optimized atlas of the images, and provides a way to access them.
+
+KorGE IntelliJ plugin will also display previews for files and atlases:
+
+![](KR.png)
+
+You can see it in action in the KorGE youtube channel with the [KorGE Chess tutorial](https://www.youtube.com/watch?v=mSK7ruZbam0&list=PLzb5P1l-LxelGV8bWyT7tnLsF96MQxqCM&index=4).
+
 ## resourcesVfs
 
 KorIO offers a `resourcesVfs` global property that holds a Virtual File System that include the

docs/korge/samples/index.md

@@ -14,6 +14,8 @@ priority: 2
 
 - [Tobse's HitKlack Remake](https://blog.korge.org/showcase-tobses-hitklack-remake/) ([play it NOW](https://tobsef.github.io/HitKlack/webstart/index.html)) ([code](https://github.com/TobseF/HitKlack))
 
+- [KorGE Chess](https://www.youtube.com/watch?v=mSK7ruZbam0&list=PLzb5P1l-LxelGV8bWyT7tnLsF96MQxqCM&index=4) ([code](https://github.com/korge-showcases/korge-chess))
+
 ## YouTube tutorials
 
 ### Korge main channel