I suppose Qt5 is common enough in Linux distros now, that most users won't have too much trouble building the latest version of Sigil all by their own big selves. But just in case ... I don't want to alienate anyone who may want to play, so I made packages for Sigil v0.8.0 that has the necessary Qt libs (Qt5.3.1) included.
Links found in the first post of the thread as usual.