API methods are not used alone, but in groups and following patterns. However, despite being a key information for API users, most usage patterns are not described in official API documents. In this article, we report a study that evaluates the feasibility of automatically enriching API documents with information on usage patterns. For this purpose, we mine and analyze 1,952 usage patterns, from a set of 396 Android applications. As part of our findings, we report that the Android API has many undocumented and non-trivial usage patterns, which can be inferred using association rule mining algorithms. We also describe a field study where a version of the original Android documentation is instrumented with the extracted usage patterns. During 17 months, this documentation received 77,863 visits from professional Android developers.