Documentation section about passing arguments to requests

[leouieda]

Description of the desired feature

Sometimes we may need to specify arguments to requests.get when downloading a file (#186 for example). This can be done with keyword arguments in HTTPDownloader. The example in the docs is passing in authentication but it would be good to say that we can pass any argument. Maybe adding a section "Passing parameters to downloaders" (or something better) after "Downloaders and authentication" to say that, in fact, we can pass anything like verify=False to skip SSL authentication (which is NOT recommended by may be required).

Are you willing to help implement and maintain this feature? Yes but welcome others to do this as well