Clarify installation on GitHub README file

When someone starts at github it's not 100% clear that a `git clone` is not the default installation method. I suspect this has confused a couple of users which makes helping them a lot more difficult.

Co-authored-by: Jaap Eldering <eldering@users.noreply.github.com>

Author: vmcj

README.md

@@ -11,6 +11,9 @@ This is the Programming Contest Jury System "DOMjudge" version 9.0.0DEV
 DOMjudge is a system for running a programming contest, like the
 ICPC regional and world championship programming contests.
 
+Installation
+------------
+We provide [stable releases](https://www.domjudge.org/download) and [daily snapshots](https://www.domjudge.org/snapshot/) of the latest code. Bootstrapping from git is an advanced use case and mostly needed for development. Installing DOMjudge is almost never done via a `git clone`, except for development use cases or testing the latest code. 
 
 Documentation
 -------------