Merge #2982

2982: Add a `rustfmt.toml` file to the repository r=epilys a=silwol

Closes: #2934

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# Description
Add a `rustfmt.toml` file to the repository, indicating to developers and tools that we use `rustfmt`. For now, it just contains a comment explaining what the file is for, and that the comment itself can be removed in case real settings are added.

# Review

- [ ] Add a short description of the change to the CHANGELOG.md file


Co-authored-by: Wolfgang Silbermayr <[email protected]>

rustfmt.toml

@@ -0,0 +1,4 @@
+# For now, this file has no contents as we don't require any specific
+# rustfmt settings. It rather serves as a marker indicating to users and
+# tools that we use rustfmt. In case you add settings to the file, feel
+# free to remove this comment.