feat: Add VSCode extension recommendation

.gitignore

@@ -7,6 +7,7 @@ exercises/clippy/Cargo.toml
 exercises/clippy/Cargo.lock
 rust-project.json
 .idea
-.vscode
+.vscode/*
+!.vscode/extensions.json
 *.iml
 *.o

.vscode/extensions.json

@@ -0,0 +1,5 @@
+{
+    "recommendations": [
+        "rust-lang.rust-analyzer"
+    ]
+}