Add links to feature docs - created TOC

[Joseph Reynolds]

On 2018-12-05 17:31, Joseph Reynolds wrote:
> I want to make it easier to find documentation for features of
> OpenBMC.  The README ... file lists the features and links to the docs
> repo, but not all features are documented there, and I'm still new to
> BMCs, so it is hard for me to determine which docs to read.
> 
> I propose to add a link from each feature to its canonical
> documentation.  So if you see me asking question in this area, you'll
> know why.

I changed the OpenBMC feature list into a table of contents for OpenBMC 
features.  The old list needed to be updated and doesn't make it easy to 
find more information about OpenBMC features.  So I looked for docs and 
added links to the project's README.

Please review.
  - Let me know what features should be added or removed, or how to
    organize the list.

  - I tried to find all the feature documentation, but I need your
    help.  Please contribute doc links for your area and I will add them.
    I prefer for each feature to link to a single document, but I will
    take what I can get.

The review is here:
https://gerrit.openbmc-project.xyz/#/c/openbmc/openbmc/+/17056/

Thanks!
- Joseph