Installation instructions for developers on Windows

Following the installation instructions for developers (https://github.com/trixi-framework/Trixi.jl?tab=readme-ov-file#for-developers) did not work on Windows 11 in powershell.
```
ERROR: UndefVarError: `..` not defined
```
We had to escape the quotes, i.e. `julia --project=. -e 'using Pkg; Pkg.develop(PackageSpec(path=\"..\"))'` worked.
Could we use another easy expression here, which works on all platforms? Something like e.g. `dirname(pwd())`?

@s6nistam

Start in the README's “For developers” installation section linked in the issue and compare the current Pkg.develop command with its behavior in PowerShell on Windows 11. Update the instruction with an expression that works across the documented platforms, then verify the command and wording on Windows and the existing developer setup path.

Written by the indexing model from the issue text.