Add README by @michaliskambi for screen_effects_blending example

examples/screen_effects/screen_effects_blending/README.md

@@ -0,0 +1,15 @@
+# Screen Effects With Blending
+
+Demo of using `TCastleScreenEffects` that sets non-trivial (not fully opaque) alpha values for the generated screen effect contents. See the [TCastleScreenEffects.Blending](https://castle-engine.io/apidoc-unstable/html/CastleScreenEffects.TCastleScreenEffects.html#Blending) API docs for a documentation.
+
+Using [Castle Game Engine](https://castle-engine.io/).
+
+## Building
+
+Compile by:
+
+- [CGE editor](https://castle-engine.io/manual_editor.php). Just use menu item _"Compile"_.
+
+- Or use [CGE command-line build tool](https://github.com/castle-engine/castle-engine/wiki/Build-Tool). Run `castle-engine compile` in this directory.
+
+- Or use [Lazarus](https://www.lazarus-ide.org/). Open in Lazarus `game_3d_sound_standalone.lpi` file and compile / run from Lazarus. Make sure to first install [CGE Lazarus packages](https://castle-engine.io/documentation.php).