Add a README to this app.
Bug: 21618018
Change-Id: I368d66da64f54a5c8200c50dc03d2990aef03be7
diff --git a/README b/README
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+Default Carrier Config App
+==========================
+
+This app works as part of com.android.phone.CarrierConfigLoader to configure telephony features
+based on the subscriber's network. It replaced many XML resource overlays in frameworks/base and
+frameworks/opt/telephony. The current framework allows per-network configuration that uses
+CarrierIdentifier objects, rather than just mcc/mnc.
+
+This app uses a CarrierIdentifier to read the appropriate config snippets from the assets folder.
+
+If you make changes to the XML files, run the unit tests to ensure they can still be parsed:
+ runtest carrierconfig-unit
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