more documentation for README.md

* short description for each service
* documenation about archive formats

README.md

@@ -10,6 +10,37 @@ This is the git repository for [openSUSE:Tools/obs-service-tar_scm](https://buil
 
 The service can be used in combination with other services like [download_files](https://github.com/openSUSE/obs-service-download_files), [extract_file](https://github.com/openSUSE/obs-service-extract_file), [recompress](https://github.com/openSUSE/obs-service-recompress) or [set_version](https://github.com/openSUSE/obs-service-set_version) e.g. within the [GIT integration](https://en.opensuse.org/openSUSE:Build_Service_Concept_SourceService#Example_2:_GIT_integration) workflow.
 
+## Archive Formats
+
+### obscpio
+The obscpio archive format is the new OBS specific archive format based on cpio which can be consumed and generated by the [OBS Delta Store](http://openbuildservice.org/help/manuals/obs-reference-guide/cha.obs.architecture.html#delta_store) to store changes in an incremental way independently from your chosen SCM.
+This is output format generated by the obs_scm service and is basically the cpio newc format.
+Additionally a file named <package>.obsinfo including useful information from your SCM system is generated, so you can access this data at buildtime.
+
+### tar
+The tar archive format creates a tarball and it is used as output format by the services "tar" and "tar_scm"
+
+## Services
+
+### tar_scm
+tar_scm is the legacy service to create a source tarball from a source code managment tool.
+
+### obs_scm
+obs_scm uses the new obscpio archive format to store the sources
+It is recommended to use obs_scm in favour to tar_scm as it helps to save a lot of disk space on the server side, especially when used in continuous integration (e.g. nightly builds etc.).
+You can use the tar service and recompress service as a buildtime service to generate the usual source tarball while buildtime.
+
+### tar
+Create a tarball out of obscpio archives
+
+### snapcraft
+The snapcraft service can be used to fetch sources before building a [snappy app](https://www.ubuntu.com/desktop/snappy).
+It parses a snapcraft.yml, for the SCM related parts and executes the corresponding services.
+
+### appimage
+The appimage service can be used to fetch sources before building a [appimage app](http://appimage.org/).
+It parses a appimage.yml for the SCM related parts and executes the corresponding services.
+
 ## Installation
 The files in this top-level directory need to be installed using the following: