libsanitizer/README.gcc update

[Kostya Serebryany <kcc at google dot com>]

Hi,

This patch updates libsanitizer/README.gcc. Ok?
(This is the first time I am trying to commit to gcc trunk)

Index: ChangeLog
===================================================================
--- ChangeLog   (revision 193693)
+++ ChangeLog   (working copy)
@@ -1,3 +1,6 @@
+2012-11-21  Kostya Serebryany  <kcc@google.com>
+        * README.gcc: Extend the README.gcc with mode details.
+
 2012-11-20  Konstantin Serebryany  <konstantin.s.serebryany@gmail.com>

        * sanitizer_common/sanitizer_linux.cc
Index: README.gcc
===================================================================
--- README.gcc  (revision 193693)
+++ README.gcc  (working copy)
@@ -1,4 +1,15 @@
-The AddressSanitizer (http://code.google.com/p/address-sanitizer) is
-a project developed by Google Inc. The source files of the project
-are hosted at http://llvm.org/svn/llvm-project/compiler-rt. These files
-are the ones in the asan subdirectory of that project.
+AddressSanitizer (http://code.google.com/p/address-sanitizer) and
+ThreadSanitizer (http://code.google.com/p/thread-sanitizer/) are
+projects initially developed by Google Inc.
+Both tools consist of a compiler module and a run-time library.
+The sources of the run-time library for these projects are hosted at
+http://llvm.org/svn/llvm-project/compiler-rt in the following directories:
+  include/sanitizer
+  lib/sanitizer_common
+  lib/interception
+  lib/asan
+  lib/tsan
+
+Trivial and urgent fixes (portability, build fixes, etc) may go directly to the
+GCC tree. All non-trivial changes, functionality improvements, etc should go
+through the upstream tree first and then be merged back to the GCC tree.