docs: Highlight migration guide and update URLs in README

Changes:
- Added prominent migration guide callout near top of README
- Updated Resources section with new docs structure URLs:
  - Tutorials: docs.datajoint.com/tutorials/
  - How-To Guides: docs.datajoint.com/how-to/
  - API Reference: docs.datajoint.com/reference/api/
  - Migration Guide: docs.datajoint.com/how-to/migrate-from-0x/
- Organized Resources section with better formatting

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

Author: dimitri-yatsenko

README.md

@@ -9,6 +9,9 @@ DataJoint is a framework for scientific data pipelines based on the **Relational
 
 **Documentation:** https://docs.datajoint.com
 
+> **📘 Upgrading from legacy DataJoint (pre-2.0)?**
+> See the **[Migration Guide](https://docs.datajoint.com/how-to/migrate-from-0x/)** for a step-by-step upgrade path.
+
 <table>
 <tr>
   <td>PyPI</td>
@@ -72,9 +75,13 @@ conda install -c conda-forge datajoint
 
 ## Resources
 
-- [Documentation & Tutorials](https://docs.datajoint.com)
-- [DataJoint Elements](https://datajoint.com/docs/elements/) — Example pipelines for neuroscience
-- [GitHub Discussions](https://github.com/datajoint/datajoint-python/discussions)
+- **[Documentation](https://docs.datajoint.com)** — Complete guides and reference
+  - [Tutorials](https://docs.datajoint.com/tutorials/) — Learn by example
+  - [How-To Guides](https://docs.datajoint.com/how-to/) — Task-oriented guides
+  - [API Reference](https://docs.datajoint.com/reference/api/) — Complete API documentation
+  - [Migration Guide](https://docs.datajoint.com/how-to/migrate-from-0x/) — Upgrade from legacy versions
+- **[DataJoint Elements](https://datajoint.com/docs/elements/)** — Example pipelines for neuroscience
+- **[GitHub Discussions](https://github.com/datajoint/datajoint-python/discussions)** — Community support
 
 ## Contributing