documentation: initial description

Add initial description of recipes in README.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>
Reviewed-by: Frédéric Dalleau <frederic.dalleau@collabora.co.uk>
Reviewed-by: Emanuele Aina <emanuele.aina@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D7205

README

@@ -2,3 +2,36 @@ General Information
 ===================
 
 Here is the recipes collection for Apertis images creation.
+
+To use these recipes, the debos tool needs to be installed: https://github.com/go-debos/debos
+
+By default, this command will create a minimal Apertis image for Intel 64bit systems:
+```
+debos apertis-ospack.yaml && debos apertis-image-amd64.yaml
+```
+
+The target architecture can be changed with command line parameter '-t architecture:armhf'.
+Architectures supported:
+  * arm64
+  * amd64
+  * armhf
+
+Packages set selection via '-t type:minimal':
+  * minimal
+  * development
+  * sdk
+
+Parameters for ospack and image versioning:
+  * suite: (-t suite:17.12)
+  * timestamp: (-t timestamp:`date +"%s"`)
+
+
+Create the ospack for the SDK package set:
+```
+debos -t type:sdk -t architecture:amd64 -t suite:17.12 --scratchsize 10G --debug-shell apertis-ospack.yaml
+```
+
+Create SDK image from prepared ospack:
+```
+debos --scratchsize 10G -t type:sdk -t suite:17.12 apertis-image-sdk.yaml
+```