WIP: add section on GitHub interface

how_to_eurec4a/howto.md

@@ -92,3 +92,32 @@ Datasets should be added by following these steps:
    A pull request can be started on the GitHub webpage. After the pull request has been submitted, the review process will start. To accellerate the process, please make sure all tests for your pull request succeed. The status of the tests are shown at the bottom of your pull request.
 
 ### via GitHub web interface 
+
+1. Visit EUREC$^4$A-Intake catalog repository
+   Go to [https://github.com/eurec4a/eurec4a-intake](https://github.com/eurec4a/eurec4a-intake)
+2. Login with your GitHub credentials
+3. Select the platform/simulation/product for which a new dataset entry shall be added
+   <img width="905" alt="image" src="https://user-images.githubusercontent.com/43613877/235442959-2aa97f47-2a56-48e2-8a33-c997fa2eeda6.png">
+4. Edit <img width="49" alt="image" src="https://user-images.githubusercontent.com/43613877/235443256-59e952c2-4d28-41af-977d-2e20435bd6ec.png">
+ `main.yaml` and add a reference to the dataset if it is simple and does not contain different subsets (e.g. resolutions, frequencies, sensors, dimensions):
+   ```yaml
+   plugins:
+      source:
+       - module: intake_xarray
+
+   sources:
+     <dataset_name>:
+       description: <short description of the dataset>
+       driver: opendap
+       args:
+         auth: null
+         urlpath: <url_to_dataset>
+         chunks: {}
+         engine: netcdf4
+    ```
+    (see 3. of **via command line** for more details
+5. Save changes and create pull request
+   <img width="1122" alt="image" src="https://user-images.githubusercontent.com/43613877/235443863-348c6f7c-0120-447f-b869-a7b280e7ad23.png">
+6. Check if the automatic tests that are run on your edits succeed. You can access the tests e.g. via the Action Tab (<img width="85" alt="image" src="https://user-images.githubusercontent.com/43613877/235444058-6319a7fd-3584-4d21-9f0a-5cd5527ea54c.png">
+).
+7. A reviewer will look at the pull request and will discuss any additional steps necessary to merge the changes to the main repository.