Add informative samples README.md

Also updates stale documentation with informative links.
diff --git a/samples/youtube/README.md b/samples/youtube/README.md
new file mode 100644
index 0000000..7c41f7a
--- /dev/null
+++ b/samples/youtube/README.md
@@ -0,0 +1,5 @@
+# Where are the samples?
+
+The YouTube API samples are now hosted separately
+from the client library project. You can find them
+[here](https://github.com/youtube/api-samples).