docs(operators): add fromPromise documentation

[niklas-wortmann]

closes: #79

[codecov-io]

Codecov Report

Merging #229 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #229   +/-   ##
=======================================
  Coverage   90.49%   90.49%           
=======================================
  Files         115      115           
  Lines         442      442           
  Branches       10       10           
=======================================
  Hits          400      400           
  Misses         40       40           
  Partials        2        2

Impacted Files	Coverage Δ
src/operator-docs/creation/fromPromise.ts	100% <ø> (ø)	:arrow_up:

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[ashwin-sureshkumar]

@btroncone - Could you please re-review ?

[niklas-wortmann]

@ashwin-sureshkumar any idea why travis is broken? there is no log or something like that

[ashwin-sureshkumar]

Its one of the dependencies @JWO719.

This PR fixes it https://github.com/ReactiveX/rxjs-docs/pull/236

Can you please review that PR, we have to have two approvals before we merge in. Then you can rebase with master and should be good.

[ladyleet]

thx @JWO719 @ashwin-sureshkumar @btroncone for all your hard work!

[niklas-wortmann]

@btroncone @ashwin-sureshkumar last commit should fix both requested changes. Please take a look at it and let me know if there is something else I can fix.

[niklas-wortmann]

@btroncone, @ashwin-sureshkumar, @sumitarora could you take another look at this pr to get this done?