docs: add tasks.task.dir

Author: SamK

website/src/docs/reference/schema.md

@@ -607,6 +607,18 @@ tasks:
       - ./deploy.sh
 ```
 
+### `dir`
+
+- **Type**: `string`
+- **Description**: The directory in which this task should run
+
+```yaml
+tasks:
+  current-dir:
+    dir: '{{.USER_WORKING_DIR}}'
+    cmd: pwd
+```
+
 #### `requires`
 
 - **Type**: `Requires`