fix(docs/index.md): Update docker badges & ocaml-sf URL

docs/index.md

@@ -7,7 +7,10 @@ lessons and tutorials.
 
 A demo is available at: [http://learn-ocaml.hackojo.org/](http://learn-ocaml.hackojo.org/).
 
-![Build status logo](https://travis-ci.org/ocaml-sf/learn-ocaml.svg)
+[![CI](https://github.com/ocaml-sf/learn-ocaml/workflows/CI/badge.svg?branch=master)](https://github.com/ocaml-sf/learn-ocaml/actions?query=workflow%3ACI)
+[![macOS](https://github.com/ocaml-sf/learn-ocaml/workflows/macOS/badge.svg?branch=master)](https://github.com/ocaml-sf/learn-ocaml/actions?query=workflow%3AmacOS)
+[![learn-ocaml](https://img.shields.io/badge/docker-ocamlsf%2Flearn--ocaml-blue.svg)](https://hub.docker.com/r/ocamlsf/learn-ocaml "Docker image of learn-ocaml")
+[![learn-ocaml-client](https://img.shields.io/badge/docker-ocamlsf%2Flearn--ocaml--client-blue.svg)](https://hub.docker.com/r/ocamlsf/learn-ocaml-client "Docker image of learn-ocaml-client")
 
 Howtos
 ------
@@ -66,7 +69,7 @@ See [https://opensource.org/licenses/BSD-3-Clause](https://opensource.org/licens
 Authors and Acknowledgements
 ----------------------------
 
-Learn-OCaml is a software by OCamlPro.
+Learn-OCaml is a free software by the [OCaml Software Foundation](https://ocaml-sf.org).
 
  * The main authors are Benjamin Canou, Çağdaş Bozman and Grégoire Henry.