Docs re-structure

[oscgonfer]

This issue is to discuss how we re-structure the docs, to give a better importance to non-techie things such as toolkits or other material that the project also works on. A proposal would be (to be discussed):

- Welcome
- Technology (better name of course)
  - Hardware
  - Firmware
  - Data
- Knowledge
  - Sensors
    - Performance
    - PM sensors
      - PMS5003
      - ...
    - Research (?)
 - Resources
   - For communities
   - For educators
   - For researchers
 - Guides
   - _Guides as they are_
 - About
   - Project philosophy
   - Funding

Would be great to have your inputs @adaisuri @pral2a @peters-rebecca