Add Hipchat Integration Examples

[TAGC]

I've spent the past hour or so trying to figure out how to send an invite over HipChat - I kept creating and trying out different HipChat API keys and getting a "Something went wrong" error. I tried looking for examples and couldn't find any. I also tried looking at your test specs and main code body.

It turns out that I needed to create a key from https://"my room".hipchat.com/account/api using the v1 API, whereas HipChat now defaults to showing you a page where you can create v2 APIs. I also needed to set the access level to "Admin" rather than "Notification".

If this is documented somewhere in the README, I think it could be helpful to new users.