docs: move architecture to user-guide

[jiacai2050]

Which issue does this PR close?

Closes #

Rationale for this change

Architecture and user guide are in different places, I think it better to place them together, so users can browse them in https://docs.ceresdb.io/

What changes are included in this PR?

• move architecture to user-guide directory in order to host via github pages
• add platform support under deploy section

Are there any user-facing changes?

Yes

How does this change test

mdbook serve locally to check everything is expected.