Update readme

Illustrate the repository's purpose and point the
reader to the api definitions.

Closes #47

README.md

@@ -2,15 +2,49 @@
 
 [![Build Status](https://travis-ci.com/wirepas/backend-apis.svg?branch=master)](https://travis-ci.com/wirepas/backend-apis)
 
-This repository contains the linux gateway protocol buffer definitions and
-language specific wrappers.
+This repository contains the message definition files for the Wirepas' 
+service APIs, specifically:
 
-Language wrappers:
+- [Wirepas Gateway][here_gateway]
+- [Wirepas Network Tool][here_wnt]
+- [Wirepas Positioning Engine][here_wpe]
 
--   [Python: wirepas_messaging][here_python]
+In addition to the the message specification files, the repository contains language specific wrappers (classes, function, ...) that simplify the translation of the API data into a target language object (see Figure 1).
+
+![runtime operation of wm-config][here_docs_operation]
+
+**Figure 1 -** Illustration of messaging wrapper's function within applications.
+
+## Language wrappers
+
+- **Python**: wirepas_messaging \[[source][here_python]\] \[[PyPi][pypi_messaging]\]
+
+## Contributing
+
+We welcome your contributions!
+
+Please read the [instructions on how to do it][here_contribution]
+and please review our [code of conduct][here_code_of_conduct].
 
 ## License
 
-Licensed under the Apache License, Version 2.0. See LICENSE for the full license text.
+Licensed under the Apache License, Version 2.0.
+See [LICENSE][here_license] for the full license text.
 
 [here_python]: https://github.com/wirepas/backend-apis/tree/master/wrappers/python
+
+[here_docs_operation]: ./docs/img/overview.png
+
+[here_gateway]: ./gateway_to_backend
+
+[here_wpe]: ./wpe
+
+[here_wnt]: ./wnt
+
+[pypi_messaging]: https://pypi.org/project/wirepas-messaging/
+
+[here_code_of_conduct]: https://github.com/wirepas/backend-apis/blob/master/CODE_OF_CONDUCT.md
+
+[here_contribution]: https://github.com/wirepas/backend-apis/blob/master/CONTRIBUTING.md
+
+[here_license]: https://github.com/wirepas/backend-apis/blob/master/LICENSE