Update the "adding a syscall" docs.

Change-Id: I78adafb1c1c491f641a82a02ad7f03cd3f8c7d1e
diff --git a/README.md b/README.md
index c6b9278..7fd903a 100644
--- a/README.md
+++ b/README.md
@@ -153,10 +153,13 @@
      the appropriate POSIX header file in libc/include/ includes the
      relevant file or files.
   4. Add function declarations to the appropriate header file.
-  5. Add at least basic tests. Even a test that deliberately supplies
+  5. Add the function name to the correct section in libc/libc.map.txt and
+     run `./libc/tools/genversion-scripts.py`.
+  6. Add at least basic tests. Even a test that deliberately supplies
      an invalid argument helps check that we're generating the right symbol
-     and have the right declaration in the header file. (And strace(1) can
-     confirm that the correct system call is being made.)
+     and have the right declaration in the header file, and that you correctly
+     updated the maps in step 5. (You can use strace(1) to confirm that the
+     correct system call is being made.)
 
 
 Updating kernel header files