You need to flash (via fastboot is the best way for me) TWRP
3.0.2.3 .
Then install (via twrp) the last version of Eu Rom with Android 6.0 release for MI5
6.11.10
The trick it's to flash de eu rom just after you boot for first time twrp, if don't, every time you reboot the global rom could change the recovery for the original.
Once you are on 6.11.10 of Eu Rom:
- Reboot TWRP
- Install Android 7.0 release
- Reboot - Never wipe /system partition manually!
- Done
- In case of any issues, make factory reset via system settings
- For ROOT on Android 7.0 install
SuperSU 2.79