Cm13 for S6 is still in alpha stage lots of stuff are broken in it you can check the bug list from XDA thread (2nd post).If you still want to install CM13 on your Galaxy S6 Follow below steps.
So lets start the guide on How to install official Cm13 custom rom in samsung Galaxy S3.We have already shared the list of devices getting official cm13 rom in our previous post.Before starting make sure that your device it rooted and having custom recovery installed in your device.
1.Download unofficial CM13 Rom for
Galaxy S6 and the appropriate Gapps 6.0 package from link given below
Copy it in your in your device.
2.Now place the Cyanogenmod 13 rom and gapps 6.0 zip file in sd card.
3.Now reboot to Custom Recovery mode(TWRP/Philz).
4.Then flash CM13 android marshmallow rom and gapps from recovery in it.
5.Now Clear cache and Clear Data.
6.Reboot your device.Done! you just flash cyanogenmod 13 rom in your Samsung Galaxy S6.Enjoy Android Marshmallow 6.0.
#Download
1.Download Cyanogenmod 13 rom for galaxy S6
(download the latest built according to date).