rename INSTALLING_FROM_SOURCE to just INSTALL

Author: henrispriet

INSTALLING_FROM_SOURCE.md renamed to INSTALL.md

@@ -31,7 +31,7 @@ Read ["Installation"] from [The Book].
 
 ## Installing from source
 
-If you really want to install from source (though this is not recommended), see [INSTALLING_FROM_SOURCE.md](INSTALLING_FROM_SOURCE.md).
+If you really want to install from source (though this is not recommended), see [INSTALL.md](INSTALL.md).
 
 ## Getting Help