Add Codespaces badge and demo installation section

README.md

@@ -13,6 +13,7 @@
 [![Quality Gate Status](https://sonarcloud.io/api/project_badges/measure?project=NatLibFi_Annif&metric=alert_status)](https://sonarcloud.io/dashboard?id=NatLibFi_Annif)
 [![docs](https://readthedocs.org/projects/annif/badge/?version=latest)](https://annif.readthedocs.io/en/latest/index.html)
 [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
+[![Open in GitHub Codespaces](https://img.shields.io/static/v1?&label=Tutorial+in+Codespaces&message=Open&color=brightgreen&logo=github)](https://codespaces.new/NatLibFi/Annif-tutorial/tree/codespaces)
 
 Annif is an automated subject indexing toolkit. It was originally created as
 a statistical automated indexing tool that used metadata from the
@@ -120,6 +121,11 @@ Start up the application:
 
  annif
 
+# Demo install in Codespaces
+Annif can be tried out in the [GitHub Codespaces](https://docs.github.com/en/codespaces). Just open a page for configuring a new codespace via the badge below, start the codespace from the green "Create codespace" button, and a terminal session will start in your browser with the contents of the [Annif-tutorial](https://github.com/NatLibFi/Annif-tutorial) repository:
+
+[![Open in GitHub Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/NatLibFi/Annif-tutorial/tree/codespaces)
+
 # Getting help
 
 Many resources are available: