📚 Umbrella README: add module table

### Description
Add a table listing all Rix modules in the main README.

### Example
| Module | Status | Version | Description |
|--------|--------|---------|-------------|
| rix-io | Stable | v1.0.0 | IO, files, buffers |

### Tasks
- [ ] Create the table  
- [ ] Add GitHub + README links  
- [ ] Indicate the default branch (`dev`)  