Add component selection documentation

[emdupre]

It would be great to have more documentation on what component selection entails. This is only covered in a very general way at this point and could be enormously expanded.

As @jbpoline had suggested, it would be great at some point to have automatically generated jupyter notebooks (using sphinx-gallery), but to start with I'd love to have a break down of the kappa, rho calculations and how various points in the decision tree impact those metrics.

One other piece: I know @handwerkerd has some examples from his meica-reports -- this section could be a great place to include those, until we generate some of our own !

[emdupre]

@jwe080, it'd be great to have your expertise here, too !

[jbteves]

Since the reorganization happening in #247 I think this issue should be paused.

[jbteves]

With #262 merged I am unpausing this issue.

[jbteves]

In line with many of the other issues I've commented on, I think that we should come up with a discrete set of tasks to close this issue. From the above, I could envision something like the following:

• Add kappa, rho calculations and decisions to readthedocs
• (Optional) Generate jupyter notebooks

[jbteves]

Given the interest in rewriting the decision tree, it seems that this issue is likely going to be solved as new code is written and documented. I think this issue is on probation.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions to tedana:tada: !