docs: Add key updates and recent updates sections to README

Restructure README with a cleaner heading and two new sections:
- Key Updates: highlights Rocky 8 migration and BC5 workflow transition
- Recent Updates: summarises recent documentation changes

Author: Climateyousheng

README.md

@@ -1,11 +1,26 @@
-# This is the home for documentation of the Bristol version of the UK Met Office Unified Model.
+# Bristol UM Documentation
+
+Documentation for the Bristol version of the UK Met Office Unified Model.
 
 [HadCM3_user_notes](HadCM3_user_notes.md)
 
 [HadCM3_technical_notes](HadCM3_technical_notes.md)
 
 [HadGEM_technical_notes](HadGEM_technical_notes.md)
 
+## Key Updates
+
+- **Rocky 8 migration** — BRIDGE servers have moved from CentOS6 to Rocky 8.10. If you haven't migrated yet, see the [Rocky 8 guide](Rocky8.md).
+- **BC5 workflow** — BC5 is replacing BC4/BP as the university HPC. See [BC5 Workflow](BC5_Workflow.md) and [University HPC](University_HPC.md) for current status and data-flow changes.
+
+## Recent Updates
+
+- **2026-02-27** — Added [CMIP7 outcomes page](CMIP7_outcomes.md) and QR code
+- **2026-02-26** — Updated CMIP7 Ozone v2.0 data
+- **2026-02-23** — Updated [University HPC](University_HPC.md) and [Model install](Model_install.md) guides
+- **2026-02-20** — Added PPE validation heatmap and regional bias sections for xqjc candidates
+- **2026-02-20** — Added [terrestrial ensemble tuning](CMIP7_soil_ensembles.md) documentation
+
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 [How to edit these pages](Editing_guide.md)