Allow running from cmd or powershell, improve bootstrap-windows.ps1, update README
cerbero: Allow running from cmd or powershell
It will simply find MSYS2 and invoke it.
cerbero: Greatly improve usability of bootstrap-windows.ps1
Instead of being a dumb list of commands, the script now does the
following:
1. Detects whether choco is already installed, and upgrades it if so.
2. Checks whether vsredist140, cmake, git, git-lfs, python3, wix,
MSYS2 are installed before trying to install them using choco.
3. If a tool is already installed but is too old, prompt before trying
to install with choco
4. Checks whether MSYS2 packages are installed before trying to
(re)install them.
5. Checks whether Visual Studio is already installed before trying to
install it.
6. If Visual Studio is installed, also check whether the Windows 11
SDK is installed. If not, prompt the user and install it.
Users can now fearlessly run `tools\bootstrap-windows.ps1` to install
or update packages.