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The user looks for documentation. He goes from the GitHub link poking around and finally finds https://github.com/nguillaumin/osmtracker-android/wiki which is apparently the documentation. I would put a direct link from the apps about page to the documentation. Also note that the Wiki page is not suitable for viewing on a cell phone because it spreads over the edge.
We can add a link, but I'm unlikely to be able to do anything about the wiki / mobile since it's a GitHub page (and I'm not keen to maintain a separate doco site)