Make README more concise and add dependency installation for externally-managed environments

[dakralex]

I had some problems while using this tool, because I run a pip installation which is externally managed by my operating system. Therefore, I needed to find the packages from my package manager. To make it easier to use the tool I added a dependency section to the README and made the README a little more concise overall, I hope you don't mind. I can revert or adapt the README in any way, if that's needed.

[Sabyasachi-Seal]

Thanks @dakralex for contributing !