docs: update copyright year

Felix Boerner

27.12.2021 ab34e460aa4700d57a3fbeeee2ae7215b1a07b8b

 README.md

@@ -179,7 +179,7 @@
Set `copyright` with the text you want for your copyright.

```toml
copyright = "©2017 Your Name"
copyright = "©2021 Your Name"
```