No comprehensive docs for `WolletDescriptor`

[ikripaka]

I tried to find comprehensive docs, but they are incomplete.
I understand that might be documented somewhere, but I can't find comprehensive doc for it.
For example docs that I found:

• blockstream.github.io - briefly mentions descriptors, giving a link to elip-150.
• elip-151 - proposes a new version of possible descriptor usage.
• elip-150 - describea the overall structure of confidential transaction descriptor.
  It refers to Descriptor, what slip77 is, adds some examples.
  But where can docs or information about defining a correct Descriptor for any transaction be obtained?.
  There appear to be far more definitions of available Descriptors when looking into the code.
• lwk_wollet WolletDescriptor - no comprehensive docs or examples for the defined type.

Steps to resolve this problem:

• Create a builder entity for the descriptor.
  The idea is not to manually introduce the descriptor like here, 1, 2, 3 ,4, etc.
  But use the builder pattern and at the last step bulid a string or type for it.
  Yep, I agree that this type can't be central, for example, for bindings, but as helper for using Rust library it can exist.
• Provide a link to existing docs where the spec can be obtained or write it for this project.