Create a README.md describing the project

The repository is missing the README.md file to describe the project.

If relevant this can then be added to the main sphinx documentation, using a direct link to the file, similarly to what's done for the [changelog.rst](https://github.com/equinor/everest-tutorials/blob/4a9d5a72a457614456293dcaba892d3bb2ca6de8/docs/source/development/changelog.rst).

Review the existing Sphinx documentation and docs/source/development/changelog.rst for the project's current documentation style and structure. Create README.md with a useful project description, and, if appropriate, add a direct link from the main Sphinx documentation; done means the README exists and the link is correct.

Written by the indexing model from the issue text.