docs: update README status to reflect implemented Phase 2 features

Changed status line from "Queries, updates, timers, and child workflows are
planned" to accurately reflect that these features are already implemented:

Implemented features now listed:
- Workflows, activities (Phase 1)
- Schedules, signals (Phase 1)
- Queries, updates (Phase 2)
- Timers (Phase 2)
- Child workflows (Phase 2)
- Continue-as-new, side effects, version markers (Phase 2)

Confirmed by source code:
- ctx.start_timer() in workflow.py
- ctx.start_child_workflow() with parent_close_policy
- client.query_workflow() and client.update_workflow()
- Worker replay loop handles all event types

Fixes #255

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: durable-workflow-ops

README.md

@@ -2,7 +2,7 @@
 
 A Python SDK for the [Durable Workflow server](https://github.com/durable-workflow/server). Speaks the server's language-neutral HTTP/JSON worker protocol — no PHP runtime required.
 
-Status: **Alpha**. Supports starting workflows, registering workers, polling workflow + activity tasks, schedules, signals, and completing workflows. Queries, updates, timers, and child workflows are planned.
+Status: **Alpha**. Core features implemented: workflows, activities, schedules, signals, queries, updates, timers, child workflows, continue-as-new, side effects, and version markers. Full language-neutral protocol support for cross-PHP/Python orchestration.
 
 ## Install