Update start_windows.cmd

[tboy1337]

Currently it doesn’t set the default branch to the same branch name as the project, setting the default branch as main wont effect users who have run the command previously and it will only take effect for new users, I’ve also added the -U flag to the pip requirements check for consistency with start_linux.sh and because specific versions of pip packages are not set in requirements.txt so its best to use the newest ones.