Add whitespace.txt file.

This is useful as a recommended way to trigger now builds
with a noop change.
I believe it's going to be used more frequently as we're closing
in on the Git switch, to test committing and pushing.

Review URL:

git-svn-id: 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/.gitignore b/.gitignore
index 05345a7..581c3bf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -122,6 +122,7 @@
diff --git a/tools/whitespace.txt b/tools/whitespace.txt
new file mode 100644
index 0000000..87c7d82
--- /dev/null
+++ b/tools/whitespace.txt
@@ -0,0 +1,9 @@
+You can modify this file to create no-op changelists.
+Try to write something funny. And please don't add trailing whitespace.
+Whitespaces are cool.
+Really cool.