Wiki docs

### Actual behavior

There are NO any tutorials/user manuals for *Astree*.

### Expected behavior

Lets start writing docs using wiki:

- Enable "Wiki" for this repo:
- https://help.github.com/en/github/building-a-strong-community/about-wikis
- https://help.github.com/en/github/building-a-strong-community/adding-or-editing-wiki-pages
- Add intro pages ("How To", "FAQ", etc.).
- Add more pages.

### REFERENCES

- https://en.wikipedia.org/wiki/Optical_engineering
- https://en.wikipedia.org/wiki/Optical_lens_design
- https://github.com/indranilsinharoy/Intro2LensDesignByGeary
- https://github.com/q4huang/First-order-optical-system-design
- https://en.wikipedia.org/wiki/Zemax#Features_and_applications
- https://en.wikipedia.org/wiki/Optics_Software_for_Layout_and_Optimization#Capabilities

Start by reviewing the linked GitHub wiki guidance and the optical-engineering, lens-design, and referenced project materials to understand Astree's documentation needs. Enable the repository wiki, create introductory How To and FAQ pages, and add further user manuals covering the project; done means the requested tutorial and reference coverage exists in the wiki.

Written by the indexing model from the issue text.