Clarify commandline usage instructions & don't double process geosonl

Nobody has claimed this yet.

Current output
```
mtsds --configure
Run mtsds with valid options:
--config filename.geojsonl,
--convert filename.geojsonl,
--sync,
--token,
or --estimate
```

Implies that the tool is looking for geojsonl as input for both `--config` and `--convert` steps. However, if I run `mtsds --config input.geojsonl` it then re-converts it, giving me `input.geojsonll`.

As a user with (most likely) a .geojson input file this is a bit confusing, esp if I haven't read the docs lately.

In summary:
- Usage should specify `.geojson` for `--config` step (and convert also?)
- [Feature Reuest] --config runs on both, only converts to geojsonl if needed (no `.geojsonll`)

Start by reproducing the reported `mtsds --config input.geojson` behavior and inspect the command-line usage plus the `--config` and `--convert` handling. Done means the usage distinguishes `.geojson` and `.geojsonl` correctly and configuring an already suitable input does not create `input.geojsonll`; clarify whether `--convert` should accept both formats.

Written by the indexing model from the issue text.