Add Contributing file

Contributions are allowed using the GitHub or GitBook interface

Author: dicortazar

CONTRIBUTING.md

@@ -0,0 +1,20 @@
+# How to contribute
+
+This book is built as a [Gitbook book](https://gitbook.com). This is written
+using [Markdown syntax](https://www.gitbook.com/book/gitbookio/markdown/).
+This is maintained under the [Daniel Izquierdo's GitHub account](https://github.com/dicortazar) in the
+[Managing Inner Source Projects repository](https://github.com/dicortazar/managing-inner-source-projects).
+
+Thus you can follow the usual contribution process in GitHub through
+[Pull Requests](https://help.github.com/articles/about-pull-requests/). You can
+see for instance the pull requests open and closed at this point in time and for
+this repository at https://github.com/dicortazar/managing-inner-source-projects/pulls .
+
+If you want to share an idea, comment or feature request, you can also open an issue
+in the [GitHub issues tracking for this repository](https://github.com/dicortazar/managing-inner-source-projects/issues).
+
+There is also another possibility and this is using the GitBook interface.
+You can [open discussions there](https://www.gitbook.com/book/dicortazar/managing-inner-source-projects/discussions).
+
+Please be aware that all of your contributions will be opened by default and
+that those will be licensed under [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/).