The learnability of an API suffers when the official documentation of the API is incomplete. Developers discuss usage scenarios of APIs in the online developer forums. As such, by automatically mining such crowd-sourced documentation of APIs, we can address the shortcomings of API official documentation. We present a framework to automatically mine usage scenarios about APIs from online developer forums. Each usage scenario of an API consists of a code example, a summary description, and the reactions (i.e., positive and negative opinions) of other developers towards the code example. We evaluate our API usage mining framework by producing a benchmark dataset. We observed a precision of 0.947 and a recall of 1.0 with the linking of a code example to an API mention in the forum.