update README after being added to Gentoo overlays

Author: r7l

README.md

@@ -4,8 +4,8 @@ Gentoo overlay with custom Ebuilds.
 
 Install using Eselect Repository:
 
-    eselect repository add r7l git https://github.com/r7l/r7l-overlay.git
+    eselect repository enable r7l
 
 Install using Layman:
 
-    layman -o https://raw.githubusercontent.com/r7l/r7l-overlay/master/overlay.xml -f -a r7l
+    layman -a r7l