Add generic install instruction for linux

[ulioidle]

The current install instructions pretty much leaves anyone not using a small handful of linux distros in the dark, you either endlessly build and respond to build failures, sift through the distro specific scripts hunting down dependencies your distro lacks, or dig through the source files to find dependencies. There should be instructions listing all dependencies which are not standard on most distros.

[dimitre]

Hello @ulioidle you can submit PRs directly to https://github.com/openframeworks/ofSite

Here is the instruction guide for linux https://github.com/openframeworks/ofSite/tree/master/files/setup/linux-install