Update repository instructions

[thibaultamartin]

Closes #2148

TODO:

• Explain how to add content to the website, and how to
  • Publish blog posts
  • Add clients
  • Add bridges
  • Add servers
  • Add integrations
  • Add SDKs
  • Add distributions Will be added when it exists
  • Add hosting services
  • Add documentation
  • Add sponsors Going to be added at a later time
• Explain how to contribute to the website
  • What are we trying to achieve with the website
  • How do we measure progress
  • How do we take decisions (encompasses "how to make sure your PR is reviewed")

[cloudflare-workers-and-pages]

Deploying matrix-website with    Cloudflare Pages

Latest commit:	61154ba
Status:	✅  Deploy successful!
Preview URL:	https://f4741403.matrix-website.pages.dev
Branch Preview URL:	https://update-instructions.matrix-website.pages.dev

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[thibaultamartin]

We have an interesting case with #2194: Syncloud is selling devices that allow people to host their own services.
They seem to rely on their own service (syncloud.it) to work around people not having static ip addresses at home.

We need to make it obvious that hosting providers need to do the hosting themselves. Syncloud seems to be more akin to a Distribution (as #2182 supports)

[MTRNord]

Note: As the distributions page isnt yet a thing /o\ (sorry :D) I will keep that one open for now until it exists.

[MTRNord]

From #2570 (review) we need to add a note about the month _index.md section files in the blog.

Done