Installation on Ubuntu 18.10+ may require libtinfo5 #408

If one is running a newer version of Ubuntu instead of the currently stable 18.04, one may need to run sudo apt-get install libtinfo5 to run Swift on Linux. This dependency is not mentioned on apple/swift under Linux and without it a user may get an error, such as: "swift: error while loading shared libraries: libtinfo.so.5: cannot open shared object file: No such file or directory".

@ematejska @saeta For the adventurous users should we add this to Installation.md even though 18.04 is the recommended distribution (which is explicitly stated)? I've tested S4TF on 19.10 and the test.swift finally works after installing libtinfo5.

Discovered the solution via https://forums.swift.org/t/using-sourcekit-lsp-on-ubuntu-18-10/22598/4.