Add the README.chromium for the symbol and source server scripts.

Review URL: http://codereview.chromium.org/155139


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@20023 0039d316-1c4b-4281-b951-d872f2087c98

tools/symsrc/README.chromium

+These files are related to the symbol and source server.
+
+This requires some Microsoft utilities.  From a 32-bit WinDbg installation with
+source server support, copy the following files to this directory:
+  dbghelp.dll
+  pdbstr.exe
+  srctool.exe
+
+The follow files were copied from the BSD licensed pefile-1.2.9.1:
+  COPYING-pefile
+  pefile.py
+
+pefile is available from:
+  http://code.google.com/p/pefile/