Add barebones README.md for Caliper to replace the old README that ha…

…d out of date information.

Also add COPYING file internally so we have one fewer file in the external repo that isn't present internally.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=176656337

README.md

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+# Caliper
+
+Caliper is a tool for measuring Java code performance, primarily focused on
+microbenchmarks.
+
+## Building
+
+To build the JVM version of Caliper (the only supported version at the moment),
+run:
+
+```shell
+mvn clean install -am -pl caliper
+```
+
+### Android
+
+Caliper currently has a number of artifacts related to Android. These are in
+a transitional state and no easy way to run Caliper benchmarks on Android is
+currently available.
+
+If you are interested in building the Android artifacts for any reason, you can
+run:
+
+```shell
+mvn clean install -am -pl caliper-android
+```
+
+Note that for these artifacts to build, you must have an `ANDROID_HOME`
+environment variable set to the location of an Android SDK containing the file
+`platforms/android-25/android.jar`. Alternatively, you can pass
+`-Dandroid.home=<path>` to your `mvn` command to set the Android SDK directory
+that way, and/or `-Dandroid.sdk.version=<version>` to specify a version other
+than `25` (but note that the build may not work with a version lower than `25`).