Add api_core package (#4210)
* Add api_core package
* Address review comments
diff --git a/README.rst b/README.rst
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index 0000000..afb4774
--- /dev/null
+++ b/README.rst
@@ -0,0 +1,14 @@
+Core Library for Google Client Libraries
+========================================
+
+|pypi| |versions|
+
+This library is not meant to stand-alone. Instead it defines
+common helpers used by all Google API clients. For more information, see the
+`documentation`_.
+
+.. |pypi| image:: https://img.shields.io/pypi/v/google-cloud-core.svg
+ :target: https://pypi.org/project/google-cloud-core/
+.. |versions| image:: https://img.shields.io/pypi/pyversions/google-cloud-core.svg
+ :target: https://pypi.org/project/google-cloud-core/
+.. _documentation: https://googlecloudplatform.github.io/google-cloud-python/latest/core/