No note about existing requirements

```
$ cabal new-build tutorial
cabal: Error parsing project file
...servant/cabal.project:50:
Parse of field 'constraints' failed.
```

Line 50 is:
```
constraints: base-compat ^>=0.11
```

After seeing https://github.com/haskell-servant/servant/issues/1176, I upgraded my Haskell installation (ghc from 8.0.1 (I think) to 8.8.3, cabal from 1.24.0.0 to 3.2.0.0, and whatever else haskell.org/ghcup does) and `cabal new-build tutorial` worked. So, at least as far as my experience goes, the issue is that, between Servant's website and the CLI, there's no note about existing requirements.