Fix pulpcore README on pypi

[CodeHeeler]

The badges weren't displaying properly.
Markdown was not being interpreted correctly and now is.

fixes #4277
https://pulp.plan.io/issues/4277

Pull Requests

Please be sure you have read our documentation regarding contributing
here:
https://docs.pulpproject.org/en/3.0/nightly/contributing/index.html

There you can read a Contribution Checklist and learn more about
appropriate branches and rebasing among other things.

Once you are ready to create a pull request:

• For properly formatting commit messages, please see the
  documentation here:
  https://docs.pulpproject.org/en/3.0/nightly/contributing/git.html#commit-message
• Once you have created your pull request, please add a link to
  your pull request into the notes/comments for the relevant bug in the
  issue tracker and change the status to POST.
• Continuous integration tests will be automatically triggered
  by your pull request. You can see the status of these tests on the
  page for your pull request. If there are failures, please try to
  fix them and update your pull request.

Thank you so much for contributing to Pulp!

[codecov]

Codecov Report

Merging #3819 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3819   +/-   ##
=======================================
  Coverage   55.68%   55.68%           
=======================================
  Files          64       64           
  Lines        2796     2796           
=======================================
  Hits         1557     1557           
  Misses       1239     1239

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[daviddavis]

LGTM