updating README to fit with the API

[stummjr]

I used the API and noticed that it behaves slightly different from the documentation. So, this PR is meant to update the documentation.

Summary of changes:

• project_ids() returns a list of integers instead of a list of strings
• project.spiders() returns a list of dicts with spider metadata instead of a list with the spider names
• schedule and project.id return an id like 123/2/12 rather than an hexa string

[eliasdorneles]

I think both versions work. :)

[stummjr]

@eliasdorneles they do work, but since the conn.project_ids() returns a list of int, it looks more consistent if we use conn[123] rather than conn['123'] in the doc.

[eliasdorneles]

fair enough!
LGTM, merging!

[nramirezuy]

I would have left an example using string since the most common task is passing the project id from the arguments of a script.