docs(procrastinate): add Procrastinate section to README

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: snopoke

README.md

@@ -41,3 +41,54 @@ taskbadger.init(
 $ export TASKBADGER_API_KEY=***
 $ taskbadger run "nightly-backup" -- ./backup.sh
 ```
+
+### Procrastinate Integration
+
+The SDK includes optional support for the [Procrastinate](https://procrastinate.readthedocs.io/) task queue.
+
+Install with the extra:
+
+```bash
+pip install 'taskbadger[procrastinate]'
+```
+
+Opt a single task into tracking with the `track` decorator:
+
+```python
+import procrastinate
+from taskbadger.procrastinate import track, current_task
+
+app = procrastinate.App(connector=...)
+
+@track
+@app.task(queue="default")
+async def add(a, b):
+    return a + b
+
+@track(name="report", value_max=100, tags={"env": "prod"})
+@app.task
+async def report(rows):
+    tb = current_task()
+    for i, row in enumerate(rows):
+        await process(row)
+        if i % 10 == 0:
+            tb.update(value=i)
+```
+
+To auto-track every task on an App, register the system integration:
+
+```python
+import taskbadger
+from taskbadger.systems.procrastinate import ProcrastinateSystemIntegration
+
+taskbadger.init(
+    token="***",
+    systems=[ProcrastinateSystemIntegration(
+        app=app,
+        auto_track_tasks=True,
+        includes=[r"myapp\..*"],
+        excludes=[r"myapp\.cleanup\..*"],
+        record_task_args=True,
+    )],
+)
+```