Purely Google refactor

PiperOrigin-RevId: 320679799
Change-Id: I6591af2c3b863d541c4cb36106d899383e8b538b

ONE_VERSION_ONLY

diff --git a/ONE_VERSION_ONLY b/ONE_VERSION_ONLY
new file mode 100644
index 0000000..a390753
--- /dev/null
+++ b/ONE_VERSION_ONLY
@@ -0,0 +1,12 @@
+Google3 requires that there be only one version of each library.
+
+For an explanation why, see:
+http://go/thirdparty#WhyOneVersion
+
+For instructions how to upgrade to a new version, see:
+http://go/thirdpartyjava
+
+If there is already more than one version here, that is a legacy issue
+and must be cleaned up as part of upgrading to a new library.
+
+Email third-party-java-owners@google.com with questions.