RRO Overlay System How-To
Download and install a compatible ROM, for N5: Frank N5 ( http://forum.xda-developers.com/google-nexus-5/development/l-android-lpv-dev-n5-enhanced-t2856934
) and Simple AOSP ( http://forum.xda-developers.com/google-nexus-5/development/rom-simpleaosp-t2933419
), Terminus ( http://forum.xda-developers.com/google-nexus-5/development/android-5-0-0r7-lrx21v-t2950499
) is coming soon
Download and install the Overlay Manager Beta from the community link (https://play.google.com/apps/testing/org.bitsyko.overlaymanager
At this point, before doing anything else, run Overlay Manager. This is critical, as it creates two folders at first run, and if you don't the rest of the instructions don't make sense.
Now you can either try some of the included sample overlays, or download some community or experimental overlays. If the overlay you download is in a zip, extract the apk and copy it to /sdcard/SykoPath-Overlays/Other Overlays then in Overlay Manager press the refresh button in the top right, then scroll down to the 'Other Overlays' section, and press 'Open Category Folder'. If it is provided as an apk, then just copy it to the 'Other Overlays' folder.
You should now have a list of files in the folder, with some details. Any activated overlays will have a blue background to make it immediately obvious that it is active. Right now you will not have any active, so there should be no blue ones. If you long press on an overlay you will get a popup FAB menu. To activate the overlay press the button that looks like two pages overlaid, or press the 3 button menu and select 'Copy Ovl(s) To /vendor/overlay'. You will get a prompt to reboot now or later. If all you want is one overlay, then you can reboot now. If you want to install multiple overlays at once, long press the first, then long press the second, etc. The check mark FAB will indicate multiple overlays selected, then you can apply them all at once.
Reboot, and you should now have the selected overlay active, and whatever it was that was themed by the overlay should now be themed.
To deactivate the overlay, similarly to activating, long press and then select the trash FAB, and then reboot.