Fix and document the verifier

[microstudi]

Fixes the verifier for ballots or election logs (a tar file).

• Verifying a single ballot requires python and the library electionguard to be installed.
• Verifying a tar election file requires java and to compile a JAR file.

I've added instructions in the README file to documentat all of this, is not ideal but it can save you a lot of time.

fixes #231
supersedes #192
requires #310 to be merged to fix the rubocop issues

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (be58cb5) 69.57% compared to head (fb1b4f4) 69.57%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #311   +/-   ##
========================================
  Coverage    69.57%   69.57%           
========================================
  Files           96       96           
  Lines         1630     1630           
========================================
  Hits          1134     1134           
  Misses         496      496           

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[andreslucena]

I just checked the installation instructions. For the moment it seems much better than what we have. There's just a minor detail to fix and we can merge this