docs: Volunteer's handbook

[jonaharagon]

Changes proposed in this PR:

• work in progress

• [x] I agree to the terms listed below:
  Contribution terms (click to expand)

  1) I am the sole author of this work. 2) I agree to grant Privacy Guides a perpetual, worldwide, non-exclusive, transferable, royalty-free, irrevocable license with the right to sublicense such rights through multiple tiers of sublicensees, to reproduce, modify, display, perform, relicense, and distribute my contribution as part of this project. 3) I have disclosed any relevant conflicts of interest in my post. 4) I agree to the Community Code of Conduct.