Update/create "governance process" documentation

[laurenluz]

we are deprecating the givgarden and should reflect that in our docs.
we should also update gov process documentation to explain how to participate in giveth dgov & how it works in an up to date way.
it would be great also to explain some of the deprecated systems and why they were deprecated (re: experments & evolution in governance)

cc @divine-comedian @WhyldWanderer @Danibelle

[oyealmond]

Do we have someone managing our documentation, if yes, is that @WhyldWanderer @Danibelle?
Im moving this issue to notion @laurenluz so you can keep track.

https://www.notion.so/giveth/Update-create-governance-process-documentation-0048e8af55d946c8b0a418c66f3383b8?pvs=4

[divine-comedian]

@oyealmond - I moved this issue to the giveth-docs repo, lets keep it here.