Explain better how to actually use the pinning service

[ec1oud]

This needed clarification IMO: I had little faith that posting random data was going to give me an auth key, but it worked. Anyway it needs to be advertised exactly how ipfs cluster can be used as a personal remote pinning service. Sorry the screenshot is so big (could be cropped if necessary), and I hope I guessed right about the path.

[hsanjuan]

You don't need to POST any data though, not even random one.