Add deploy_env_gerenation README.md -> kameleon

addons/deploy_env_generation/README.md

+It is now advised to use [kameleon](https://kameleon.imag.fr) for the construction of the deployment mini-OS.
+
+Kameleon is an builder of operating systems, based on recipes.
+
+Recipes for the kadeploy mini-OS can be found in the [Grid'5000 environment recipes](https://gitlab.inria.fr/grid5000/environments-recipes/-/tree/master/kadeploy3-deploy-kernel?ref_type=heads) repository.
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+Other methods (e.g. based on debirf) are not maintained.