[Docs]: Improvements to the LangChain Documentation

[MinuraPunchihewa]

Short description of what should be added or improved

There are a few issues/concerns with the LangChain documentation,

1. The parameters CREATE ML_ENGINE command in the Setup section is bounded by square brackets. I am not sure if this is intentional, but it might be confusing.

2. Prompt templates require at least one placeholder ({{}}). In the examples given for each type of provider, none have been used.

3. In the Describe Data section, the tool_based_agent created previously has been used to describe a table a connected data source. Is it possible to do this without specifying a tool? I cannot seem to do so. The same model has been used for similar operations in the sections that follow.
   

4. The simple model that has been created here (tool_based_agent) can also be used to run simple 'predictions'. Should we add an example of this and include tools in a different section? For example, we can run simple predictions like this one like we would with OpenAI (without providing USING args) and that might be a good starting point before diving into tools?
   

Video or screenshots

No response

Anything else?

No response

[MinuraPunchihewa]

@martyna-mindsdb I've fixed the minor issues (1 and 2 from above) here:
#9344

What are your thoughts on 3 and 4?

[martyna-mindsdb]

@MinuraPunchihewa
Yes. We can start with a "SELECT without USING", or we can enclose the USING clause in the square brackets to mark it as optional.