Docs new section

[Borda]

What does this PR do?

add new section in changelog and fix hr

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

[SkafteNicki]

While we are fixing readme, maybe also change the github reference in the bibtex, seems outdated:

​@Article​{​falcon2019pytorch​,
  ​title​=​{​PyTorch Lightning​}​,
  ​author​=​{​Falcon, WA​}​,
  ​journal​=​{​GitHub. Note: https://github. com/williamFalcon/pytorch-lightning Cited by​}​,
  ​volume​=​{​3​}​,
  ​year​=​{​2019​}​
}
Should be https://github.com/PyTorchLightning/pytorch-lightning

[codecov]

Codecov Report

Merging #2236 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #2236   +/-   ##
======================================
  Coverage      88%     88%           
======================================
  Files          70      70           
  Lines        5435    5435           
======================================
  Hits         4775    4775           
  Misses        660     660           

[Borda]

@williamFalcon lets merge this one and all new (add new HR in docs) do in followup PR