Add notes for windows users

It is not possible to execute the bootstrap.sh from cygwin

    Maximilian@Maximilian /cygdrive/c/Sententiaregum/vagrant
    $ bootstrap.sh
    ./bootstrap.sh: line 2: $'\r': Kommando nicht gefunden.
    : Ungültige Optionne 3: set: -
    set: usage: set [--abefhkmnptuvxBCHP] [-o option] [arg ...]
    ./bootstrap.sh: line 4: $'\r': Kommando nicht gefunden.
    ./bootstrap.sh: line 6: Syntaxfehler im bedingen Ausdruck.
    '/bootstrap.sh: line 6: Syntaxfehler beim unerwarteten Wort `]]
    '/bootstrap.sh: line 6: `if [[ "$OSTYPE" == *darwin* || "$OSTYPE" == *msys* ]]


So I've copied the devstack.yaml manually.

I've checked out this just4fun on cmd.exe and the interesting thing was that it worked:
    C:\>cd Sententiaregum/vagrant
    
    C:\Sententiaregum\vagrant>bootstrap.sh
    Welcome to Git (version 1.8.5.2-preview20131230)
    
    
    Run 'git help git' to display the help index.
    Run 'git help <command>' to display help for specific commands.
    [bootstrap] link Vagrantfile to project root
    [bootstrap] link .vagrant to project root
    ln: `/c/Sententiaregum/vagrant/../.vagrant': cannot overwrite di
    [bootstrap] create devstack.yaml in project root
    cp: overwrite `/c/Sententiaregum/vagrant/../devstack.yaml'? n

So I've added that note