This example show how to manage two KSP installs, like one on your Windows gaming rig and one on your Mac, as they were one.
First, create a GitHub repo called git-ksp-ckan
under your own username
Then, if your Mac is the starting point:
cd ~/Library/Application Support/Steam/SteamApps/common/Kerbal Space Program
git init
cp CKAN/installed-default.ckan CKAN/should-be-installed.ckan
git add CKAN/should-be-installed.ckan
echo "saves/scenarios" >> .gitignore
echo "saves/training" >> .gitignore
git add .gitignore
git add saves
Create a commit with the date and time as message
git commit -a -m $(date "+%Y%m%d%H%M")
git remote add origin https://github.com/<yourusername>/git-ksp-ckan.git
Push the changes up to GitHub
git push -u origin master
Now on your Windows PC start "Git Bash"
First we make sure ckan.exe is in the KSP folder
cd "/c/Program Files (x86)/Steam/SteamApps/Common/Kerbal Space Program"
cp /c/Users/<yourusername>/Downloads/ckan.exe .
ckan.exe update
Then we add our Git repository and fetch the files
git init
git remote add origin https://github.com/<yourusername>/git-ksp-ckan.git
git fetch --all
git reset --hard origin/master
Now it's time to make sure CKAN is correctly up to date
ckan.exe install -c CKAN/should-be-installed.ckan
You should now be able to start KSP, see your old saves and ships, and have all the right mods installed.