Add a basic description for CentOS adapted from the existing description and some basic copy from Wikipedia

centos/README-short.txt

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+The official build of CentOS.
+

centos/README.md

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+# Supported tags and respective `Dockerfile` links
+
+- [`latest`, `centos7` (*docker/Dockerfile*)](https://github.com/CentOS/sig-cloud-instance-images/blob/af7a1b9f8f30744360a10fe44c53a1591bef26f9/docker/Dockerfile)
+- [`centos6` (*docker/Dockerfile*)](https://github.com/CentOS/sig-cloud-instance-images/blob/8717e33ea5432ecb33d7ecefe8452a973715d037/docker/Dockerfile)
+- [`centos5` (*docker/Dockerfile*)](https://github.com/CentOS/sig-cloud-instance-images/blob/2e5a9c4e8b7191b393822e4b9e98820db5638a77/docker/Dockerfile)
+
+# CentOS
+
+CentOS (abbreviated from Community Enterprise Operating System) is a Linux
+distribution that attempts to provide a free, enterprise-class,
+community-supported computing platform which aims to be 100% binary compatible
+with its upstream source, Red Hat Enterprise Linux (RHEL). In January 2014, it
+was announced that CentOS was officially joining forces with Red Hat while
+staying independent from RHEL, under a new CentOS Governing Board.
+
+> [wikipedia.org/wiki/CentOS](https://en.wikipedia.org/wiki/CentOS)
+
+This is the official CentOS image, and will be updated on a regular schedule or
+as needed for emergency fixes.
+
+The `centos:latest` tag will always point to the most recent version currently
+available, and `centos:6` will point to the latest version of the CentOS 6 tree.
+
+![logo](https://raw.githubusercontent.com/docker-library/docs/master/centos/logo.png)
+
+# User Feedback
+
+## Issues
+
+If you have any problems with or questions about this image, please contact us
+ by submitting a ticket at [https://bugs.centos.org](https://bugs.centos.org) or through a [GitHub issue](https://github.com/CentOS/sig-cloud-instance-images/issues).
+
+You can also reach many of the official image maintainers via the
+`#docker-library` IRC channel on [Freenode](https://freenode.net).
+
+## Contributing
+
+You are invited to contribute new features, fixes, or updates, large or small;
+we are always thrilled to receive pull requests, and do our best to process them
+as fast as we can.
+
+Before you start to code, we recommend discussing your plans by submitting a ticket at [https://bugs.centos.org](https://bugs.centos.org) or 
+through a [GitHub issue](https://github.com/CentOS/sig-cloud-instance-images/issues), especially for more ambitious
+contributions. This gives other contributors a chance to point you in the right
+direction, give you feedback on your design, and help you find out if someone
+else is working on the same thing.

centos/content.md

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+# CentOS
+
+CentOS (abbreviated from Community Enterprise Operating System) is a Linux
+distribution that attempts to provide a free, enterprise-class,
+community-supported computing platform which aims to be 100% binary compatible
+with its upstream source, Red Hat Enterprise Linux (RHEL). In January 2014, it
+was announced that CentOS was officially joining forces with Red Hat while
+staying independent from RHEL, under a new CentOS Governing Board.
+
+> [wikipedia.org/wiki/CentOS](https://en.wikipedia.org/wiki/CentOS)
+
+This is the official CentOS image, and will be updated on a regular schedule or
+as needed for emergency fixes.
+
+The `centos:latest` tag will always point to the most recent version currently
+available, and `centos:6` will point to the latest version of the CentOS 6 tree.
+
+%%LOGO%%

centos/mailing-list.md

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+by submitting a ticket at [https://bugs.centos.org](https://bugs.centos.org) or