Move the Rust tutorial into a sub-directory

To make room for the C++ version next to it :-)

docs/tutorial/rust/src/memory_tile.md

@@ -0,0 +1,32 @@
+# Memory Tile
+
+With the skeleton in place, let's look at the first element of the game, the memory tile. It will be the
+visual building block that consists of an underlying filled rectangle background, the icon image. Later we'll add a
+covering rectangle that acts as a curtain. The background rectangle is declared to be 64 logical pixels wide and tall,
+and it is filled with a soothing tone of blue. Note how lengths in the `.60` language have a unit, here
+the `px` suffix. That makes the code easier to read and the compiler can detect when your're accidentally
+mixing values with different units attached to them.
+
+We copy the following code inside of the `sixtyfps!` macro:
+
+```60
+{{#include main_memory_tile.rs:tile}}
+```
+
+Inside the <span class="hljs-built_in">Rectangle</span> we place an <span class="hljs-built_in">Image</span> element that
+loads an icon with the <span class="hljs-built_in">@image-url()</span> macro. The path is relative to the folder in which
+the `Cargo.toml` is located. This icon and others we're going to use later need to be installed first. You can download a
+[Zip archive](https://sixtyfps.io/blog/memory-game-tutorial/icons.zip) that we have prepared and extract it with the
+following two commands:
+
+```sh
+curl -O https://sixtyfps.io/blog/memory-game-tutorial/icons.zip
+unzip icons.zip
+```
+
+This should unpack an `icons` directory containing a bunch of icons.
+
+Running the program with `cargo run` gives us a window on the screen that shows the icon of a bus on a
+blue background.
+    
+![Screenshot of the first tile](https://sixtyfps.io/blog/memory-game-tutorial/memory-tile.png "Memory Tile Screenshot")