Add example of LVM cache creation
Add example of LVM cache creation

Useful for testing as well as for users wondering how to do something like this.

AdamWill/blivet,vpodzime/blivet,jkonecny12/blivet,vojtechtrefny/blivet,rhinstaller/blivet,jkonecny12/blivet,vojtechtrefny/blivet,AdamWill/blivet,rvykydal/blivet,rhinstaller/blivet,rvykydal/blivet,vpodzime/blivet