Add a README with some basic instructions.

README.md

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+<!--
+SPDX-FileCopyrightText: 2023 Diego Elio Pettenò
+
+SPDX-License-Identifier: 0BSD
+-->
+
+# IPv6 In Real Life (Generator)
+
+This is the backend, generator part of [IPv6 In Real Life].
+The website is project by [Flameeyes] to track the usefulness of an IPv6 network across a number
+of different services and classes of sites.
+
+For a background and details of what this project is about see [the launch blog post].
+
+## Contributing
+
+To contribute information for a new country or expand an existing country, edit or create the JSON
+files inside `ipv6_in_real_life/data/`.
+
+For each country there has to be a directory with the lowercase [ISO 3166-1 alpha-2] code, inside
+which there has to be an empty `__init__.py` file.
+Within these directories there should be one JSON file per category, according to the already
+existing categories for other countries.
+
+The format of the JSON file should follow:
+
+```
+[
+ {
+ "main_host": "www.someservice.example",
+ "additional_hosts": [
+ "users.someservice.example",
+ "login.someservice.example"
+ ]
+ }
+]
+```
+
+Include additional hosts that are necessary to make use of the service, for instance an user area
+or the authentication host. If no additional hosts are necessary, omit the field.
+
+Please follow the [REUSE] specifications, including a `.license` file next to the existing JSON
+files.
+
+## Additional Repositories
+
+The [IPv6 In Real Life] website is rendered from the frontend available at
+https://github.com/Flameeyes/ipv6-in-real-life-frontend.
+
+
+[IPv6 In Real Life]: https://ipv6-in-real.life/?mtm_campaign=social&mtm_kwd=github&mtm_cid=ipv6-in-real-life
+[Flameeyes]: https://flameeyes.blog/?mtm_campaign=social&mtm_kwd=github&mtm_cid=ipv6-in-real-life
+[the launch blog post]: https://flameeyes.blog/2023/04/30/ipv6-in-real-life/?mtm_campaign=social&mtm_kwd=github&mtm_cid=ipv6-in-real-life
+[ISO 3166-1 alpha-2]: https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
+[REUSE]: https://reuse.software/