README: describe LD and LTO variables

Demonstrate how to use the mold linker
and how to enable link time optimization.

The mold linker is the only one that directly supports
lone's new embedding capabilities at the moment.

README.md

@@ -18,13 +18,17 @@ Lone is built by a simple GNU Make file.
 The following commands can be used:
 
     make
-    make lone
     make clean
-    make clean lone
-    make lone CFLAGS=-g
-    make lone UAPI=/alternative/linux/uapi/headers
-    make lone TARGET=x86_64 UAPI=/linux/uapi/headers/x86_64
+    make lone
     make tools
+    make clean lone
+    make clean lone tools
+
+    make CFLAGS=-g
+    make LD=mold
+    make LTO=yes
+    make UAPI=/alternative/linux/uapi/headers
+    make TARGET=x86_64 UAPI=/linux/uapi/headers/x86_64
 
 Currently supported targets: