Restructure Miden compiler documentation

[Dominik Schmid]

We need to adjust the docs for the Miden compiler a bit

As described in 0xPolygonMiden/miden-base#472, we want documentation for the Miden compiler. The source files of the documentation should be located in the Compiler repo. Then, developers can update the docs using the same PR as the code.

Target group for the Miden compiler docs

We have different target groups for our documentation:

1. People who want to develop on top of Polygon Miden - e.g., write new smart contracts (accounts, notes), build new applications, etc. For them, we need in-depth tutorials and examples.
2. People who want to use Polygon Miden. For now, this is mostly people who may want to play with it - but in the future, it can be people who want to participate in running the network.
3. People who want to contribute to Polygon Miden - e.g., those who may be interested in making proposals to improve the compiler or contribute to the development etc.

For now, the order of importance is the above. That means the docs should be super clear about how to write a Miden smart contract or Miden note. The DevRel team around @gubloon can help with feedback for 1.

Proposed structure

• let's discuss / settle on a structure in this issue

Mkdocs

We are going to use Mkdocs and a plugin to build the Miden unified docs in docs.polygon.technology.

So please build the docs with mkdocs material already in mind.