Mention git clone command in the INSTALL.md

INSTALL.md

@@ -6,7 +6,11 @@ You can directly download the [latest binaries for
 linux](https://git8.cs.fau.de/software/copar/-/jobs/artifacts/master/download?job=test).
 
 ## Build from source
-In order to compile it from source
+In order to compile it from source, download the sources via:
+
+    git clone https://git8.cs.fau.de/software/copar.git
+    
+In the then created `copar` directory, run
 
     stack build