Add documentation for preview datasets in Kedro-viz

docs/source/visualisation/preview_datasets.md

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+# Preview data in Kedro-Viz
+
+This page describes how to preview data from different datasets in a Kedro project with Kedro-Viz. Kedro-viz currently supports preview of `CSVDatasets` and `ExcelDatasets`
+
+
+We use the [spaceflights tutorial](../tutorial/spaceflights_tutorial.md) and demonstrate how to add data preview for the `customer`, `shuttle` and `reviews` datasets. Even if you have not yet worked through the tutorial, you can still follow this example; you'll need to use the [Kedro starter for the spaceflights tutorial](https://github.com/kedro-org/kedro-starters/tree/main/spaceflights) to generate a copy of the project with working code in place.
+
+If you haven't installed Kedro [follow the documentation to get set up](../get_started/install.md).
+
+Then, in your terminal window, navigate to the folder you want to store the project.
+
+Generate a copy of the spaceflights tutorial project with all the code in place by using the [Kedro starter for the spaceflights tutorial](https://github.com/kedro-org/kedro-starters/tree/main/spaceflights):
+
+```bash
+kedro new --starter=spaceflights
+```
+
+When prompted for a project name, you can enter anything, but we will assume `Spaceflights` throughout.
+
+When your project is ready, navigate to the root directory of the project.
+
+### Configure the Data Catalog
+
+Kedro-viz currently supports preview of two types of datasets:
+
+* `pandas.CSVDataset` 
+* `pandas.ExcelDataset`
+
+
+To enable the preview of these datasets, you need to add the `preview_args` attribute to the `kedro-viz` configuration under the `metadata` section in the Data Catalog:
+
+```yaml
+companies:
+  type: pandas.CSVDataSet
+  filepath: data/01_raw/companies.csv
+  metadata:
+    kedro-viz:
+      layer: raw
+      preview_args:
+          nrows: 5
+
+reviews:
+  type: pandas.CSVDataSet
+  filepath: data/01_raw/reviews.csv
+  metadata:
+    kedro-viz:
+      layer: raw
+      preview_args:
+          nrows: 10
+
+shuttles:
+  type: pandas.ExcelDataSet
+  filepath: data/01_raw/shuttles.xlsx
+  metadata:
+    kedro-viz:
+      layer: raw
+      preview_args:
+          nrows: 15
+```
+
+
+
+### Previewing Data on Kedro-viz 
+
+After you've configured the Data Catalog, you can preview the datasets on Kedro-Viz. Start Kedro-Viz by running the following command in your terminal:
+
+```bash
+kedro viz
+```
+
+The previews are shown as follows:
+
+Click on each dataset node see a small preview in the metadata panel:
+
+
+![](../meta/images/preview_datasets_metadata.png)
+
+
+View the larger preview of the dataset by clicking the `Expand Preview Table` button on the bottom of the metadata panel.
+
+
+![](../meta/images/preview_datasets_expanded.png)
+
+