Meltano: Add installation instructions for target-jsonl-blob executable

## Description

The `cratedb-to-file` Meltano example includes a `target-jsonl-blob` loader configuration in `framework/meltano/cratedb-to-file/meltano.yml` that references a local executable (`./target-jsonl-blob`), but there are no instructions on how to obtain or build this binary.

## Tasks

- Add installation/setup instructions to the README or a separate INSTALL.md file
- Document how to download or build the `target-jsonl-blob` binary
- Include source repository, build commands, or release URLs
- Explain the executable path configuration and the `bucket` config example

## Related Files

- `framework/meltano/cratedb-to-file/meltano.yml` (lines 105-115)
- `framework/meltano/cratedb-to-file/README.md`

## References

- PR: https://github.com/crate/cratedb-examples/pull/1368
- Comment: https://github.com/crate/cratedb-examples/pull/1368#discussion_r2727319964
- Upstream repository: https://github.com/MeltanoLabs/target-jsonl-blob

Requested by: @amotl