docs: Improve Contributing Guide

[dplewis]

New Pull Request Checklist

• I am not disclosing a vulnerability.
• I am creating this PR in reference to an issue.

Approach

• Document Helper::print. PHPUnit doesn't allow echo, var_dump, print_r to output to STDOUT
• Remove unused links
• Remove unused cloud code folder
• Add Code of Conduct

TODOs before merging

• Add changes to documentation (guides, repository pages, in-code descriptions)

[parse-github-assistant]

Thanks for opening this pull request!

• ❌ Please link an issue that describes the reason for this pull request, otherwise your pull request will be closed. Make sure to write it as Closes: #123 in the PR description, so I can recognize it.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (a0957c1) 98.48% compared to head (f6de82c) 98.48%.

❗ Current head f6de82c differs from pull request most recent head 6491f5e. Consider uploading reports for the commit 6491f5e to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #508   +/-   ##
=========================================
  Coverage     98.48%   98.48%           
  Complexity     1060     1060           
=========================================
  Files            38       38           
  Lines          3225     3225           
=========================================
  Hits           3176     3176           
  Misses           49       49           

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[mtrezza]

Looks good, is this ready for merge?

[parseplatformorg]

🎉 This change has been released in version 2.2.0