Add main, test for Rail Fence Cipher and update README.md

[Krounosity]

• [☑️] I have read CONTRIBUTING.md.
• [☑️] This pull request is all my own work -- I have not plagiarized it.
• [☑️] All filenames are in PascalCase.
• [☑️] All functions and variable names follow Java naming conventions.
• [☑️] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• [☑️] All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.70%. Comparing base (3e10f8f) to head (1052019).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5761      +/-   ##
============================================
+ Coverage     66.57%   66.70%   +0.12%     
- Complexity     4451     4477      +26     
============================================
  Files           606      607       +1     
  Lines         16839    16901      +62     
  Branches       3240     3259      +19     
============================================
+ Hits          11211    11273      +62     
  Misses         5181     5181              
  Partials        447      447              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[siriak]

Looks good, thanks!

[Krounosity]

Looks good, thanks!

Thank you!