Create a README and pubspec for the front_end package.

pkg/front_end/README.md

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+# Front end for Dart
+
+This package provides a low-level API for use by compiler back ends that wish to
+implement the Dart language.  It is intended for eventual use by dev_compiler,
+dart2js, and the Dart VM.  In addition, it will share implementation details
+with the analyzer package--this will be accomplished by having the analyzer
+package import (and re-export) parts of this package's private implementation.
+
+End-users should use the [dartanalyzer][analyzercli] command-line tool to
+analyze their Dart code.
+
+Integrators that want to write tools that analyze Dart code should use the
+[analyzer] package.