add Readme

Readme.md

+# Useful Containers for my CI Endeavours
+
+## How to use
+
+Command-line:
+```
+docker login hub.cs.upb.de/lukasngl/container
+docker pull hub.cs.upb.de/lukasngl/container/<image>
+```
+
+In `gitlab-ci.yml`:
+```yaml
+myjob:
+	image: hub.cs.upb.de/lukasngl/container/<image>
+```
+
+## Pandoc `<image> = pandoc`
+
+Pandoc provides [great containers](https://github.com/pandoc/dockerfiles),
+but the entry point is not `/bin/sh -c`, so I would have to set an ugly
+image value in my otherwise beautiful `gitlab-ci.yml` files.
+
+
+## LaTex `<image> = latex-<variant>`
+
+### Base `<variant> = base`
+
+Pandoc even provides a quite compact LaTex distribution, which we can use as a
+base. We again have to set the entry point and enable further installation of
+packages by adding `tlmgr` to the path.
+
+### With Common Packages `<variant> = common`
+
+I will add all non-obscure packages to this, that I commonly need.