Add run script, and VSCode build task

.vscode/tasks.json

@@ -0,0 +1,21 @@
+{
+    // See https://go.microsoft.com/fwlink/?LinkId=733558
+    // for the documentation about the tasks.json format
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "cargo watch",
+            "type": "shell",
+            "command": "bin/run",
+            "args": [],
+            "problemMatcher": [],
+            "group": {
+                "kind": "build",
+                "isDefault": true
+            },
+            "runOptions": {
+                "runOn": "folderOpen"
+            }
+        }
+    ]
+}

README.md

@@ -37,3 +37,5 @@ nix-shell --run 'cargo run'
 # build
 nix-build
 ```
+
+There is a also a `bin/run` script which starts 'cargo watch'; and it is used by VSCode as well (`Ctrl+Shift+B`).

bin/run

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+set -xe
+exec nix-shell --run 'cargo watch -x run'