put migration doc under the user guide section
that's where I meant to put in the first place but got it wrong somehow
- [#[timestamp]](./timestamp.md)
- [#[global_logger]](./global-logger.md)
- [Printers](./printers.md)
+ - [Migrating from git defmt to stable defmt](./migration.md)
- [Design & impl details](./design.md)
- [Interning](./interning.md)
- [Dealing with duplicates](./duplicates.md)
- [Deserialization](./deserialization.md)
- [Log frames](./log-frame.md)
- [Lookup](./lookup.md)
-- [Migrating from git defmt to stable defmt](./migration.md)
