[doc] Update document for vector store.

[wenjin272]

No

Purpose of change

Update document for vector store.

Tests

No

API

No

Documentation

• doc-needed
• doc-not-needed
• doc-included

[xintongsong]

@wenjin272
After adding the collection and document management operations, the overall structure of this doc become a bit weird.

I'd suggest to re-organize the structure as follows:

• Overview
  • use cases: practically current content of the overview section
  • concepts / terminology: explain what is collection & document
• How to use
  • declare: decorators & resource descriptors
  • query
  • manage collections
  • manage documents
• bulit-in providers
• custom providers

The text contents look good to me.

[xintongsong]

This code snippet is an example of MyVectorStore that implements BaseVectorStore. It's not an interface declaration. In that sense, implementation should be provided for all these methods.

The implementation can be a simple demonstration, like:

def size(self, ...):
    size = ...
    return size

or

def delete(self, ...):
    // delete the document
    pass