Create shell scripts to install per distro dependencies for build

[MarioHewardt]

To make it easier/faster, create shell scripts on a per distro basis that installs all the required dependencies.

[juju4]

Per the monodevelop requirements in README.md, only Ubuntu 18.04 seems to be possible for build
https://www.monodevelop.com/download/ has no build for Ubuntu 20.04 or RHEL/Centos 8...

[kesheldr]

@juju4 The Ubuntu 18.04 instructions (the same as in the README) work on Ubuntu 20.04. RHEL/Centos 8 instructions will be updated in due course.

[MarioHewardt]

I've removed the dependency on Mono and updated all the build instructions.