GeoSearch module documentation is available for transclusion via Special: ApiHelp on Wikipedia:
https://en.wikipedia.org/w/api.php?action=help&modules=query%2Bgeosearch
But, the same is not true for MediaWiki (
https://www.mediawiki.org/w/api.php?action=help&modules=query%2Bgeosearch results in badmodule error)
Not sure why, but I'm wondering if it has something to do with the fact that GeoData extension is not installed on MediaWiki..