feat: start documenting dataset administration

docs/dataset.md

 # Dataset administration
 
+The main interest of ANIS is to browse datasets from, eventually multiple, databases.
+Instances can access datasets when properly configured.
+
+This page details the configuration possibilities of datasets by focusing on the examples provided with the **default instance**.
+
+Click on the **instance settings (gear)** to land on the *dataset administration page* of the default instance.
+
+Note that you can organize datasets into so-called *families*.
+For instance for the default instance, you can see the *default dataset family*, *the SVOM family*, and the *IRIS dataset family*.
+
+You can obviously add another dataset family by clicking the top green button *New dataset family*.
+
+![new_dataset_family](img/new_dataset_family.png)
+
+Once you get some dataset families you can add and configure some datasets.
+
+You can delete a dataset family by clicking on the **deletion button (red
+bin)** of the family, **the deletion is irreversible**.
+
+On a dataset card, you can see 4 buttons, as on [the page with the instances](web_admin.md#web-interface).
+
+ - **dataset settings (gear)**: to [configure](#dataset-settings) *the datasets and web-pages* in the instance
+ - **dataset edition (pencil)**: to [configure](#dataset-edition) the instance *intrinsic properties* themselves
+ - **dataset export (file export)**: to *[export](#import-and-export) the instance configuration*
+ - **dataset deletion (bin)**: to *delete the dataset itself*, **an irreversible operation**
+
+![dataset_configuration](img/dataset_configuration.png)
+
 ## Dataset settings
 
+Under construction.
+
 ## Dataset edition
 
-## Dataset export
+If you click the **dataset edition (pencil)** button. You should land on a page
+resembling the form for the instance edition.
+
+The form should be self-explanatory, detailing all the main properties of the chosen dataset.
+
+Changing the latter configuration, changes the main properties of the chosen instance.
+Hence, changes to the latter form should be registered cautiously.
+
+**Note**: once changes completed, don't forget to click in **Update dataset
+information** validation button *at the bottom of the page*, to register the
+latter.
+
+## Import and export
+
+### Dataset export
+
+If you click the **dataset export (file export)** button, you should get a
+popup proposing the download of the chosen dataset configuration via a `json`
+file.
+
+The latter file is useful when you want to [import](#dataset-import) the
+configuration from elsewhere, for example a production environment.
+
+### Dataset import
+
+Say you wish to create a new dataset, and you have a `json` configuration file at your disposal.
+
+You can click in the *green card with a plus sign* on the administration portal in a dataset family.
+
+![dataset_import](img/dataset_import.png)
+
+From there, you can either fill a form that resembles the one offered via **dataset edition**.
+Or, you can choose the button **Import an instance**, that offers to select a `json` configuration file on click and **Import a dataset**.
+
+If no error occurs, the new instance should be available for further configuration.