`stable` and `dev` channels

[XVilka]

Currently, we have only one channel - master, which is deployed to https://book.rizin.re. I suggest:

• Use the same branching scheme as other Rizin projects - stable and dev
• Deploy stable on https://book.rizin.re/
• Deploy dev on https://book-dev.rizin.re/ or a similar domain
• See .github/workflow/mdbook.yml for branch settings (also update the base)
• Update Rizin release checklist issue template to include the step of tagging the book too (optional?)
• Point Rizin site to two version of the books - stable and dev

[wargio]

probably we should drop this, and embed the book into the main repo and then autogen the online website at each release (i.e. tag)

[ret2libc]

@wargio book embedded into main code? I don't like it too much, there's plenty of stuff here.

[wargio]

no, i mean embedded in the rizin repo.
We can have images, etc.. here. just text in the main repo.

[XVilka]

I agree with @ret2libc - it's better to keep it separate.