#142 Add description of quick look

README.md

@@ -13,3 +13,35 @@ DESHIMA code for data analysis
 ```shell
 pip install decode==2.10.0
 ```
+
+## Quick look
+
+de:code ships with a quick look command `decode-qlook`, which will be available from the CUI after installation. It has several subcommands for each observation type. For example, to quick-look at a raster observation:
+```shell
+$ decode-qlook raster /path/to/dems.zarr.zip
+```
+where `dems.zarr.zip` is the merged observation data ([DESHIMA measurement set: DEMS](https://github.com/deshima-dev/dems)) to be checked. By default, it will output an image of the result plots by a simple analysis (e.g. continuum map, etc). You can also get the result data themselves by changing the output format:
+```shell
+$ decode-qlook raster /path/to/dems.zarr.zip --format zarr.zip
+```
+See the command help for all available options:
+```shell
+# list of the subcommands and descriptions
+$ decode-qlook --help
+
+# list of the available command options
+$ decode-qlook raster --help
+```
+
+If you are not sure about the observation type, the `auto` subcommand may be useful to automatically select the appropriate command to use:
+```shell
+$ decode-qlook auto /path/to/dems.zarr.zip
+```
+
+Finally, all subcommands are available as functions in the `qlook` submodule. For example, the `raster` command corresponds to `decode.qlook.raster` and the following Python code is equivalent to the CUI:
+```python
+import decode
+
+decode.qlook.raster("/path/to/dems.zarr.zip")
+```
+See [the qlook module documentation](https://deshima-dev.github.io/decode/_apidoc/decode.qlook.html) for more information.