depot_tools: Update README file to point to bootstrap/gclient.sh/.bat instead of

bootstrap/update.sh

BUG=38130
TEST=None

Review URL: http://codereview.chromium.org/2818011

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@50099 0039d316-1c4b-4281-b951-d872f2087c98

README

@@ -33,7 +33,7 @@ This package contains:
 Note: svn and python will be installed automatically if not accessible (on
 Windows only).
 
-To update this distribution manually, run bootstrap\update.bat on Windows,
-or bootstrap/update.sh on Linux or Mac.
+To update this distribution manually, run bootstrap\gclient.bat on Windows,
+or bootstrap/gclient.sh on Linux or Mac.
 
 To disable automatic updating, set the environment variable DEPOT_TOOLS_UPDATE=0