Please provide an AppImage for Linux

Continuation of https://github.com/HelloZeroNet/ZeroNet/issues/283 (we were told that this issue belongs into this project here).

Start by reading the linked ZeroNet issue #283 and then inspect ZeroBundle's packaging and release entry points; the issue names no files or tests. Done means producing and documenting a working AppImage for Linux, with its required ZeroNet dependencies bundled.

索引モデルが issue の本文から書いたものです。