Updated README following PR #215

[vifor2]

Update README.md following this PR.

• Removed the mentions that Python 2.7 & 3.4 are supported since we will be getting rid of them for the next release.
• Now telling the user to configure MFA themselves following @j4v's changes.
• No longer telling the user they can identify with a CSV file since it has been removed.

[zer0x64]

Not sure how to deal with the "Python2 will be deprecated" in the current release, but other than that it's good!

[codecov-io]

Codecov Report

Merging #223 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #223   +/-   ##
========================================
  Coverage    30.47%   30.47%           
========================================
  Files           73       73           
  Lines         5067     5067           
========================================
  Hits          1544     1544           
  Misses        3523     3523

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[x4v13r64]

Not sure how to deal with the "Python2 will be deprecated" in the current release, but other than that it's good!

I'd say update the readme with a warning and make it clear in the release notes. All of the refactoring will likely be released under a 5.0.0 number, so we can make a big deal of all the changes.