The link was pointing to a not very helpful page in the x-api repo.
It's now pointing to the contributing guide in the docs repo.

This is no longer desireable, since GitHub shows license information on the repo homepage
based on the LICENSE file, provided that it can detect the license. We're using the MIT
license directly from choosealicense.com, which is maintained by GitHub, so the license is
properly detected.

* Add Gitter badge

- trimmed a bunch: the fewer words used, the more words read.
- removed step-by-step full setup in favor of referring to the CI
  script.

- fixed a couple typos too.

- was: "problems", now: "tracks"
- help has been deprecated; update links.

Needed to run the x-api, locally.

the github styles already have ruling lines for h1 and h2s.