Add descriptions to all projects with README files

These show up in the project manager when hovering over projects.

viewport/2d_in_3d/project.godot

@@ -16,6 +16,7 @@ _global_script_class_icons={
 [application]
 
 config/name="2D in 3D"
+config/description="A demo showing how a 2D scene can be shown within a 3D one using viewports."
 run/main_scene="res://2D_in_3D.tscn"
 config/icon="res://icon.png"
 

viewport/3d_in_2d/project.godot

@@ -16,6 +16,7 @@ _global_script_class_icons={
 [application]
 
 config/name="3D in 2D"
+config/description="A demo showing how a 3D scene can be shown within a 2D one using viewports."
 run/main_scene="res://3d_in_2d.tscn"
 config/icon="res://icon.png"
 

viewport/3d_scaling/project.godot

@@ -16,6 +16,15 @@ _global_script_class_icons={
 [application]
 
 config/name="3D Viewport Scaling"
+config/description="This demo shows how to scale the 3D viewport rendering without affecting
+2D elements such as the HUD. It also demonstrates how to toggle filtering
+on a viewport by using TextureRect to display the ViewportTexture
+delivered by the Viewport node. This technique can be useful in 2D games
+as well. For instance, it can be used to have a 'pixel art' viewport for
+the main game area and a non-pixel-art viewport for HUD elements.
+
+ViewportContainer can also be used to display a viewport in a GUI, but it
+doesn't offer the ability to enable filtering."
 run/main_scene="res://hud.tscn"
 config/icon="res://icon.png"
 

viewport/dynamic_split_screen/project.godot

@@ -16,6 +16,8 @@ _global_script_class_icons={
 [application]
 
 config/name="Dynamic Split Screen"
+config/description="This sample project showcases an implementation of dynamic
+split screen, also called Voronoi split screen, using GDSL."
 run/main_scene="res://SplitScreen.tscn"
 config/icon="res://icon.png"
 

viewport/gui_in_3d/project.godot

@@ -16,6 +16,8 @@ _global_script_class_icons={
 [application]
 
 config/name="GUI in 3D"
+config/description="A demo showing a GUI instanced within a 3D scene using viewports,
+as well as forwarding mouse and keyboard input to the GUI."
 run/main_scene="res://gui_in_3d.tscn"
 config/icon="res://icon.png"
 

viewport/screen_capture/project.godot

@@ -16,6 +16,7 @@ _global_script_class_icons={
 [application]
 
 config/name="Screen Capture"
+config/description="An example showing how to take screenshots of the screen."
 run/main_scene="res://screen_capture.tscn"
 config/icon="res://icon.png"