Add a README for tuner HAL.

Test: viewed on gtiles.
Change-Id: Ib03bd9ffecd0c67a504a129db7b1cf16181f7b1f
diff --git a/tv/tuner/README.md b/tv/tuner/README.md
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+# Tuner HALs
+
+## Overview
+
+TV specific tuners.
+
+Sett 1.0/ITuner.hal for an overview.
+
+*** note
+**Warning:** The HALs are not (yet) frozen, as the HAL definition is
+expected to evolve between Android releases.
+***