Fix instructions to generate .DEPS.git

DEPS

 # This file is automatically processed to create .DEPS.git which is the file
 # that gclient uses under git.
 #
 # See http://code.google.com/p/chromium/wiki/UsingGit
 #
 # To test manually, run:
-#   python tools/deps2git/deps2git.py -o .DEPS.git
+#   python tools/deps2git/deps2git.py -o .DEPS.git -w <gclientdir>
 #   gclient runhooks
+# where <gcliendir> is the absolute path to the directory containing the
+# .gclient file (the parent of "src").
 # DO NOT CHECK IN CHANGES TO .DEPS.git. It will be automatically updated by
 # a bot when you modify this one.
 #
 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 
 vars = {
   # Use this googlecode_url variable only if there is an internal mirror for it.
   # If you do not know, use the full path while defining your new deps entry.
   "googlecode_url": "http://%s.googlecode.com/svn",
@@ skipping 736 matching lines @@
                 "-s", "src/build/linux/bin/eu-strip.sha1",
     ],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "name": "gyp",
     "pattern": ".",
     "action": ["python", "src/build/gyp_chromium"],
   },
 ]