Create SOURCES.md

[spy-t]

#11

[baziotis]

Thanks for the PR! Unfortunately I'm not sure about this one. Maybe just keeping a discussion thread is better than listing the resources into a file. This because probably people will disagree on what's the best resource to learn from. I'm leaving this open though if at some point we arrive at a list of resources that we all think is good and also keep the discussion thread for other resources.

[spy-t]

Noted. Although I think sources chosen by people like you who have previous experience with the subject can't go wrong, I agree that an open discussion might be better in the long run.

[baziotis]

I partially agree but also people like me don't necessarily have useful opinions. :) Also, experienced programmers might disagree with each other. With the discussion, if one cares about anyone's specific opinions, they can read their posts and it's a win-win.