[docs] Simplify WSL2 installation steps (#3246)
[docs] Simplify WSL2 installation steps (#3246)

* Simplify WSL2 installation steps
- The wsl --install command was backported to Windows 2004 and higher. This drastically simplifies installation of WSL2. https://devblogs.microsoft.com/commandline/install-wsl-with-a-single-command-now-available-in-windows-10-version-2004-and-higher/
- Windows 10 1903 and 1909 are out of support at the moment of writing (https://docs.microsoft.com/en-us/windows/release-health/release-information), and also don't support the wsl --install command. Therefore we don't mention them anymore in the installation guide.

rfay/ddev,rfay/ddev,rfay/ddev,drud/ddev,rfay/ddev,drud/ddev,drud/ddev,drud/ddev,drud/ddev,rfay/ddev