[DOC] Improve the overall deployment documentation

[alainncls]

In order to improve the developer experience, we need to improve the documentation in the main README file to describe what needs to be done to start supporting a new network, linking to the READMEs for the contracts, the subgraph, the SDK and the Explorer.

[Tomiwa1]

Hey @alainncls, kindly assign this to me.

[alainncls]

Hey @alainncls, kindly assign this to me.

Done!
Bear in mind that #859, #860 and #861 are not done yet.

[Tomiwa1]

hey @alainncls, I raised a PR already.

If this is approved, I think I can jump on #859, #860, and #861. I realized they are all linked.