Finished the API documentation

docs/api/work.md

 ## Work
+
+### GET `/work` [requires authentication]
+
+Get the information on the currently open work item of the authenticated user. If no item is open,
+404 will be returned.
+
+#### Response body
+
+```typescript
+interface Body {
+    status: string;
+    work: {
+        id: string;
+        task: string;
+        user: string;
+        started: number;
+        finished?: number;
+    };
+}
+```
+
+### POST `/work/start` [requires authentication]
+
+Create a new work item with the given data.  All open work items for the authenticated user will
+also be closed in turn.  On successful creation the id of the new work item will be returned.
+
+#### Request body
+
+```typescript
+interface Body {
+    task: string;
+}
+```
+
+#### Response body
+
+```typescript
+interface Body {
+    status: string;
+    id: string;
+}
+```
+
+### PUT `/work/finish` [requires authentication]
+
+Finish the currently open work of the authenticated user. If no item is open, 404 will be returned.
+