Documentation updates

[azvoleff]

• Under Features - UNCCD reporting
  • [x] Review and update all content, add links to UNCCD reporting manual
  • [x] Update SDG 15.3.1 tables (new color coding, @gdaldegan)
  • [x] Add SO2 (@gdaldegan)
  • [x] Add SO3 (@gdaldegan)
• Training manual - UNCCD reporting
  • [x] Add SO2 (@gdaldegan)
  • [x] Add SO3 (@gdaldegan)
• Other
  • [ ] Review all images to update for latest version (@MLNoon)
  • [x] Update FAQ (@MLNoon)
  • [ ] Add documentation for carbon tool (@MLNoon)
  • [x] Add documentation for metadata tool (@azvoleff)
  • [x] Add documentation for reports tool (@azvoleff)
  • [x] Update publications list (@azvoleff)
  • [ ] Update changelog (@azvoleff)
  • [x] Add note that now need 3.22

[azvoleff]

@gabrieldaldegan @MLNoon - can you update your progress here?

[gdaldegan]

I have finished the first version of the documentation for SO2 & SO3 background and step-by-step. Now revising these and updating the publication list.