update README.md

README.md

@@ -3,16 +3,25 @@ This is the README for gtkballs.
 
 ## Requirements
 
- - a working X11 setup
- - gtk+ version 2.x
+ - GTK 2 >= 2.14 / GTK 3
 
 ## Compiling
 
-```
-$ ./autogen.sh
-$ ./configure
-$ make
-```
+Run
+
+- ./autogen.sh
+- ./configure --prefix=/usr
+- make
+
+By default the GTK3 port is compiled, use `--enable-gtk2`
+or `--disable-gtk3` to compile the GTK2 port.
+
+- ./configure --prefix=/usr --enable-gtk3
+
+The GTK3 version provides HiDPI support with:
+
+- `GDK_SCALE=2 ./gtkballs` - make UI 2x bigger
+- `GDK_SCALE=3 ./gtkballs` - make UI 3x bigger
 
 ## Installing