docs: Adding Greenpass to USERS list

[edernucci]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Optional. My organization is added to USERS.md.
• I've signed the CLA and my build is green (troubleshooting builds).

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #3699 into master will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3699      +/-   ##
==========================================
- Coverage   41.50%   41.39%   -0.12%     
==========================================
  Files         115      115              
  Lines       16540    16540              
==========================================
- Hits         6865     6846      -19     
- Misses       8785     8808      +23     
+ Partials      890      886       -4     

Impacted Files	Coverage Δ
controller/appcontroller.go	43.72% <0.00%> (-2.37%)	⬇️

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[alexmt]

Thank you @edernucci !