Samsung S2 GT 9100 marshmallow 6.0.1 custom

Basic first time installation instructions:
Download CM-13.0-XXXXXXXX-NIGHTLY-i9100.zip to your sdcard
Make sure you're using a Kitkat Compatible Recovery
Boot into Recovery
Wipe all your data
Flash CM-13.0-XXXXXXXX-NIGHTLY-i9100.zip from sdcard
(Optional)Flash Google Apps.zip from sdcard
Reboot

file to download 

Rom CyanogenMod official nightly builds:
http://download.cyanogenmod.org/?device=i9100

Google Apps:
https://wiki.cyanogenmod.org/w/Google_Apps

For i9105p Download Rom
Here