Add owners file to GN bootstrap.

Add comment to the top of the script to clarify support and to suggest the type of thing that usually goes wrong.

Review URL: https://codereview.chromium.org/1528863004

Cr-Original-Commit-Position: refs/heads/master@{#365290}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 484f322506039ab63ddfbcf3820932f561e5a0f9

tools/gn/bootstrap/OWNERS

diff --git a/tools/gn/bootstrap/OWNERS b/tools/gn/bootstrap/OWNERS
new file mode 100644
index 0000000..72e8ffc
--- /dev/null
+++ b/tools/gn/bootstrap/OWNERS
@@ -0,0 +1 @@
+*

tools/gn/bootstrap/bootstrap.py

diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index 6a6d12d..967c80d 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -3,6 +3,12 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# This file isn't officially supported by the Chromium project. It's maintained
+# on a best-effort basis by volunteers, so some things may be broken from time
+# to time. If you encounter errors, it's most often due to files in base that
+# have been added or moved since somebody last tried this script. Generally
+# such errors are easy to diagnose.
+
 """Bootstraps gn.
 
 It is done by first building it manually in a temporary directory, then building