Add documentation for Scientfic Linux

sl/README-short.txt

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+Official containers for Scientific Linux(SL)

sl/content.md

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+# Scientific Linux
+
+%%LOGO%%
+
+These images contain [Scientific Linux](http://www.scientificlinux.org/).
+
+## About Scientific Linux
+
+Scientific Linux is a [Fermilab](http://fnal.gov/) sponsored project.  Our primary user base is within the High Energy and High Intensity Physics community.  However, our users come from a wide variety of industries with various use cases all over the globe – and sometimes off of it!
+
+Our Mission:
+> Driven by Fermilab’s scientific mission and focusing on the changing needs of experimental facilities, Scientific Linux should provide a world class environment for scientific computing needs.
+
+Scientific Linux is a rebuild of Red Hat Enterprise Linux (property of Red Hat Inc. NYSE:RHT).
+
+Please see [About Scientific Linux](http://www.scientificlinux.org/about/) and [Why Make Scientific Linux](http://www.scientificlinux.org/about/why-make-scientific-linux/) for more information.
+
+## Container Tags
+
+A tag will be provided for each of the [maintained major releases](http://www.scientificlinux.org/downloads/sl-versions/) of Scientific Linux (`6`, `7`).
+
+The `latest` tag will track the highest version numbered release of Scientific Linux.
+
+Updated images will be released roughly once per month.
+
+## Build Process
+
+The root filesystem for these docker images is built on our internal build system.
+
+## Getting Help
+
+* [SL Faq](https://www.scientificlinux.org/documentation/faq)
+
+* [Email Lists](https://www.scientificlinux.org/community)
+
+## Docker, overlayfs, and yum
+
+Recent Docker versions support the [overlayfs](https://docs.docker.com/engine/userguide/storagedriver/overlayfs-driver/) backend, which is enabled by default on most distros supporting it from Docker 1.13 onwards. On SL 6 and 7, that backend requires `yum-plugin-ovl` to be installed and enabled, which it is in our containers. Make it sure you retain the `plugins=1` option in `/etc/yum.conf` if you update that file; otherwise, you may encounter errors related to rpmdb checksum failure - see [Docker ticket 10180](https://github.com/docker/docker/issues/10180) for more details.
+
+## Package docs and licence files
+
+By default the SL docker images do not include these files.  If you require them, please remove `tsflags=nodocs` from `/etc/yum.conf` and run `yum reinstall mypackage` to recieve the documentation.
+
+---
+# Quick Reference
+
+## Example Usage
+You can try out the containers via:
+
+```console
+$ docker pull %%IMAGE%%
+$ docker run -it %%IMAGE%%:6 cat /etc/redhat-release
+$ docker run -it %%IMAGE%%:7 cat /etc/redhat-release
+```
+
+## Enabling systemd in SL7
+The SL7 docker container ships with systemd mostly functional.  You can build a SL7 systemd enabled container with the following Dockerfile
+
+In order to run a container with systemd, you will need to mount the cgroups volumes from the host.
+
+```Dockerfile
+# Example SL7 systemd Dockerfile
+FROM %%IMAGE%%:7
+ENV container docker
+### This example enables httpd via systemd within the container
+RUN yum -y install httpd && yum clean all && systemctl enable httpd.service
+EXPOSE 80
+### End of example commands for httpd via systemd
+VOLUME [ "/sys/fs/cgroup" ]
+CMD ["/usr/sbin/init"]
+```
+
+You can build and run this example (with apache) via:
+```console
+$ docker build --rm -t local/mycontainer your/path
+$ docker run -ti -v /sys/fs/cgroup:/sys/fs/cgroup:ro -p 80:80 local/mycontainer
+```
+Which will run systemd within the container in a limited context.
+
+It is recommended that you install any relevant [OCI hooks](https://www.opencontainers.org/) for your container host - such as `oci-register-machine` or `oci-systemd-hook`.
+
+Some container hosts must add `--tmpfs /run` to the `docker run` command.
+

sl/github-repo

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+https://github.com/scientificlinux/sl-docker

sl/maintainer.md

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+[Scientific Linux Development Team](%%GITHUB-REPO%%)