Link to documentation in the original repositories

[gabrieldansereau]

@tpoisot The links to the documentation in the original repositories are broken, but I can't fix them since they have been archived. Raising this here since it would be a good thing to fix them until the monorepo is ready.

The links that need to be updated (in the README and the About section):

• SimpleSDMLayers.jl: https://poisotlab.github.io/SimpleSDMLayers.jl/stable/
• GBIF.jl: https://poisotlab.github.io/GBIF.jl/stable/
• Fauxcurrences.jl: https://poisotlab.github.io/Fauxcurrences.jl/

[tpoisot]

Good catch, the full documentation will point to a single website, so the problem will take care of itself (I've also updated the README to point to this repo).