Document dependence on binutils

[fedarko]

See #552. The root cause of that issue was binutils not being installed before trying to install EMPress (installing iow involves running the ar command, which is included with binutils).

I suspect that binutils should be installed by default on most Unix systems, so this problem will likely only be an issue for very minimal Linux distributions (e.g. Damn Small Linux, which -- at least in 2007 -- didn't include binutils) or for setups like Windows Subsystem for Linux (WSL) (WSL was used in #552).

This information should probably go alongside the information from #550 -- IMO the easiest way to do this would be adding a "Installation FAQ/Troubleshooting" subsection the end of the "Installation & Basic Usage" section of the README.