Enhanced installation instructions

List of changes to README:
- I enhanced the README file to the following general outline: 
   - The fist section describes the general system-independent steps and notes one can also just download a pre-built binary
   - the second section is a table with a dependency overview, containing more info and rationales for the dependencies thus effectively informing the end-user of what he/she is installing and why
   - the third and final section consists of the platform specific "copy-paste ready" instructions
- links to the release binary now point to https://github.com/GijsTimmers/kotnetcli/releases/latest instead of hardlinking to a specific version
- changed the headers Markdown syntax (just not familiar with the other format; don't know whether or not it's "valid")
- Added the full non-abbreviated name to the description for clarity: *KotNet Command Line Interface*
- linked to the [kuleuven page describing KotNet](https://admin.kuleuven.be/icts/english/kotnet)

I think the installation instructions are clearer and more informative now. Of course you'll have to see what you want to keep and you can still change it.

Also some more questions I went into when writing the dependencies rationales:

 - does kotnetcli use python2 specific things or should it also run fine in a python3 environment? If so, this can be added in the dependency description table
 - do you need a python interpreter for running the pre-built binary? I assumed not and stated it this way in the dependency overview table
 - I have no idea of availability of the dependencies on Windows, if needed...