docs: improve command line environment variable tips (#16490)

Co-authored-by: Michael H <git@riskymh.dev>

docs/guides/runtime/set-env.md

@@ -28,10 +28,21 @@ BAR=world
 
 Variables can also be set via the command line.
 
-```sh
+{% codetabs %}
+
+```sh#Linux/macOS
 $ FOO=helloworld bun run dev
 ```
 
+```sh#Windows
+# Using CMD
+$ set FOO=helloworld && bun run dev
+
+# Using PowerShell
+$ $env:FOO="helloworld"; bun run dev
+```
+
+{% /codetabs %}
 ---
 
 See [Docs > Runtime > Environment variables](https://bun.sh/docs/runtime/env) for more information on using environment variables with Bun.

docs/runtime/env.md

@@ -15,10 +15,40 @@ BAR=world
 
 Variables can also be set via the command line.
 
-```sh
+{% codetabs %}
+
+```sh#Linux/macOS
 $ FOO=helloworld bun run dev
 ```
 
+```sh#Windows
+# Using CMD
+$ set FOO=helloworld && bun run dev
+
+# Using PowerShell
+$ $env:FOO="helloworld"; bun run dev
+```
+
+{% /codetabs %}
+
+{% details summary="Cross-platform solution with Windows" %}
+
+For a cross-platform solution, you can use [bun shell](https://bun.sh/docs/runtime/shell). For example, the `bun exec` command.
+
+```sh
+$ bun exec 'FOO=helloworld bun run dev'
+```
+
+On Windows, `package.json` scripts called with `bun run` will automatically use the **bun shell**, making the following also cross-platform.
+
+```json#package.json
+"scripts": {
+  "dev": "NODE_ENV=development bun --watch app.ts",
+},
+```
+
+{% /details %}
+
 Or programmatically by assigning a property to `process.env`.
 
 ```ts