I was just about to finally buy into the iCloud Photo Library storage (for my MacBook Pro, iPhone 6, and iPad Air), but as I was doing this on my macBook, it said I must have latest OS, which is El Capitan. I have Yosemite and I'm not ready to risk El Capitan yet. Does this mean I cannot store all my photos in iCloud Photo Library, making them available in the Photos program/app on my computer and devices?