Update structure of SUMMARY.md

[phklive]

Updated structure to make Miden book work

[phklive]

@greenhat @bitwalker could you guys see if this updated structure works for you.

[phklive]

The new structure requires that we have an index.md for each section see example here: https://github.com/0xPolygonMiden/miden-base/blob/main/docs/index.md

the ones we need to fill here are:

• usage/index.md
• appendix/index.md
• guildes/index.md
• design/index.md

Could you guys help me fill out these files, they are just an introduction to what the user will be able to find in this chapter.

[greenhat]

I'm on it.

EDIT: #422

[greenhat]

Looking great! Thank you!

[greenhat]

@phklive I'm going to merge this PR and fill the index.md #422 in a new PR ASAP.

[phklive]

Would it be possible to merge those into main please @greenhat?

Or would we need to wait for the next release?

I think that we should maybe re-open this PR with the base branch as main in that case.

[greenhat]

@phklive we merged next to main 6 months ago, so it's very outdated. We're planning to make a release in the upcoming days and merge next to main.
Theoretically, we could merge to main only the docs folder, but since the docs describe the compiler version that in the next branch anyway, it does not make sense.

[phklive]

Okay great!

Could we make sure to merge this PR + the index PR + to make a release before the eow please guys @greenhat @bitwalker

[greenhat]

That's our plan.