Make common/README.txt more succinct
This will get copied into other samples, and I don't want to
scare users away from the sample they're currently browsing.
diff --git a/common/README.txt b/common/README.txt
index 1f28b00..1320cfc 100644
@@ -1,4 +1 @@
This directory contains shared classes referenced by some samples.
-If you're exploring the samples, we recommend you start in the other