Move the Rust tutorial into a sub-directory

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

docs/tutorial/rust/src/SUMMARY.md

@@ -0,0 +1,12 @@
+# Summary
+
+- [Introduction](./introduction.md)
+- [Getting Started](./getting_started.md)
+- [Memory Tile](./memory_tile.md)
+- [Polishing the Tile](./polishing_the_tile.md)
+- [From One To Multiple Tiles](./from_one_to_multiple_tiles.md)
+- [Creating The Tiles From Rust](./creating_the_tiles_from_rust.md)
+- [Game Logic In Rust](./game_logic_in_rust.md)
+- [Ideas For The Reader](./ideas_for_the_reader.md)
+- [Running In A Browser Using WebAssembly](./running_in_a_browser.md)
+- [Conclusion](./conclusion.md)