Fix missing DESTDIR from example

README.md

 
     $ git clone <url-to-mkit>
     $ cd mkit
-    $ make install <path/to/myproj>
+    $ make install DESTDIR=<path/to/myproj>
     $ echo 'MKIT_DIR=utils/mkit'          >> Makefile
     $ echo 'include $(MKIT_DIR)/mkit.mk'  >> Makefile
     $ git add .